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Do you want to switch to SI units?
8

Do you want to switch to SI units?

Do you want to switch to SI units?

(OP)
As title asks.

RE: Do you want to switch to SI units?

Could you provide some context for your question?  From the fact that you have indicated that you work in the 'Aerospace' sector I can understand why you may be asking this question but I would like to hear you say it first.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

Pretty sure this has been discussed before.

By many measures the metric system has some advantages over 'US customary' however, they are often (in my opinion & having used both my entire career) significantly overstated.

While true believers may not want to hear this, some folk espouse that there may be a few disadvantages to the metric V US system.

(Plus keep in mind, as implied so subtly by Pat this site is not US only so many members are already metrified.)

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Do you want to switch to SI units?

If you are using one system you do not want to switch to another.
 I was working in the UK when they went metric and it was not seamless or painless. Anybody got a 6.34mm bolt?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

Nope, not at all.

RE: Do you want to switch to SI units?

Will a 6.35mm do berkshire?

Pat, according to my Director I have 'people skills' - not sure my old manager would have agreed but there you go.  

(Then again, I'm pretty sure it was my directors way of saying 'Ken you're a bit of dumb a$$ but vaguely useful and as we can't hire any new folk quickly right now and I need someone to dump the project management of these horrible tasks on to...')

Remind me, how much is a third of a meter?  A third of a foot or yard is easy.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Do you want to switch to SI units?

Well I was working for a British company here in the states when the UK went through 'decimalization' and while it had no direct effect on us, I can remember reading the group newspaper where there would be articles about how to avoid being ripped-off at the 'green grocers', both when you were looking at the units of measure of what you were buying as well as making sure that you got the correct change back.

And BTW, working for that British company we were told to say 'Imperial' units, as they frowned on the term 'English' units as it made it sound like they were somehow to blame winky smile  

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

Kenat,
We can play that game.  How much is 1/5 of a foot or yard?  That's easy for a metre.

RE: Do you want to switch to SI units?

Ken.
Close enough unless you want to go for 6.345.
And I would rather have an imperial pint.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

Blast.  Now I want cake.

RE: Do you want to switch to SI units?

We went officially in 1970 in Aus but it was really gathering momentum in 1974. Having a lab/scientific background, I found it easier than most, but must admit that 40 years on I still use imperial for some measures.

The real pain was in the early 80s where some cars had engines, transmissions and bodies built in different parts of the world and used different bolt stds on different parts. What bolts do you use to bolt an American gearbox to a Japanese made engine to go into an Australian made car. If it's imperial will it be Whitworth or SAE. If it's metric will it be Japanese or European metric.

Regards
Pat
See FAQ731-376: Eng-Tips.com Forum Policies for tips on use of eng-tips by professional engineers &
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RE: Do you want to switch to SI units?

Back in the 60's, when I was in engineering school, we had to deal with both schemes on nearly a daily basis.  It was sort of a joke as a US highway split the campus in half (it has since been diverted, bypassing most of the area) with the majority of the science classes being held in buildings on one side of the road while the engineering buildings were all on the other side.  So as you walked across the highway between classes (trying to avoid getting hit by an 18-wheeler) you would move from SI/Metric units to Imperial/English/Traditional units.  And the amazing thing is that NO one, faculty or student, ever really commented that much about the absurdity of the situation, except for the highway acting as a sort of 'barrier' between these two 'worlds'.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

John,
How many wheels does a metric 18 wheeler have?

Hokie,
1/5 of a foot is no tougher than 1/6 of a meter.

I teach a lot of classes to pretty mixed audiences all over the world and I've gotten tired of fighting over system names.  I now label one column "SI" and the other I follow the JM Campbell convention and use "fps" for "feet, pounds, seconds".  It isn't exactly right (since oilfield units and psi don't fit the fps system, and dyne/cm is not SI), but I don't have to argue about whether it is "English", "Imperial", "Old", or just "dumb".

I always ask a new class what units do they use for natural gas production volumes.  I get such a range of answers (in one class of 20, I got 13 different units).  In the U.S. the basic volume is MSCF/day.  In Canada it is E3m3/day (thousands of cubic meters, at "standard" conditions is implied but the standard is anything but).  In Australia they pretend that all gas is 1000 BTU/SCF and convert to Joules (an MJ is an MCF with that silly assumption).  I think it was Namibia that used kg/hr, which really makes the most sense to me but everyone else wants to use volumes tied to a rock (STP or some variant).  After about half way around the room we always agree that MSCF works for more of us that any alternative.  Almost no one like m^3/day because the numbers are too damn small.

David   

RE: Do you want to switch to SI units?

"The great thing about standards is there are so many to choose from." <author unknown>

This is just my humble opinion, but this whole issue of which standard should America be using today would be moot if the Aerospace industry didn't depend so much on selling military hardware, which is basically purchased by a single customer, the Federal government, whose procurement processes are still rooted in the last century (and I don't necessarily mean the 20th).  This was the basis for my rather snarky remark to the OP of this thread when I noted that he had self-identified as working in the 'Aerospace' industry and this was probably WHY he was asking a question of this nature.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

David, you mentioned 18 wheelers...

Well speaking of 'wheels', the 'rims' are designed and sized based on Imperial/English untis while the 'tires' are Metric.  

And every mass produced automotive sparkplug ever manufactured was Metric, even 60 years ago when every other nut and bolt on an American-built car or truck was Imperial/English units (why do you think sets of SAE wrenches always came with special sockets designated for 'Sparkplugs').

But on the other hand, fire-hydrants and the standard for firehose connections are based on Imperial/English units.  Sometimes absolute assurance of interchangeability is more important than complying with the local units of measure.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

SI unifies electrical, mechanical and thermal analysis with no nasty conversion factors. So easy to simulate whole systems using it. You have to cope with rad/s for shaft speeds, but that's not a difficult leap to make.

Ask me what I weigh in kg though, and I'd need to think about it.

- Steve
 

RE: Do you want to switch to SI units?

Further to the question about 18 wheelers.  Apparently, the answer is 22.  In Australia, all of the big trucks have 3 axles on the trailers.

zdas, maybe you missed the post where KENAT started that.  He used 1/3, you used 1/6.  Same riddle.

RE: Do you want to switch to SI units?

I need to do my calcs in SI to avoid forgetting a g sub c somewhere. What the )(*$ kind of unit system doesn't even allow you to calculate F = m*a without using a conversion factor?

I then convert the results to a unit my commonsense is calibrated in.

We work in THREE systems here:  SI and derived metric units, US customary units, and Imperial units.
 

RE: Do you want to switch to SI units?

We were taught that F was proportional to m*a in physics classes at the age of about 13 and did loads of experiments to demonstrate it. A big light switched on in my brain when I finally realised that in SI units, not only was F proportional to m*a, it was actually equal to it.

- Steve
 

RE: Do you want to switch to SI units?

Pat,
When pressure is reported in kg/m^2, you need a metric version of g(c).  I see more gagues with that silly unit these days than kPa or bar.  Welcome to my world.

David

RE: Do you want to switch to SI units?

So did zero experience chuck this bomb over the fence and then run?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

Who's up for several of 5.7 deciliters of Guinness???   Nope, just doesn't sound right!

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Do you want to switch to SI units?

It doesn't, hence the use of terms like a litre of milk but a pint of beer.

I still like to use psi or bar for pressure. I don't even know what the tables are that David refers to. Boiling point vs pressure maybe? I like psi because I can envisage it graphically in my mind and I am accustomed to it's effect on tyres. I like bar because it is a simple multiplier of atmospheric pressure for forced induction engines.

If we used deg K instead of C I guess temperature changes in gasses from pressurisation would become a bit easier.

This could go all year though.

Ultimately we use what we have at hand and learn the conversions if really necessary.

Regards
Pat
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RE: Do you want to switch to SI units?

Pat,
I'm talking about classroom materials.  Things like the units that an empirical equation needs in fps in one column and the units in SI in another, or a tablulation of a physiscal parameter like saturation quantity of water in natural gas vs. pressure for a constant temperature.

Your bar example works in a lot of the world, but I always find myself in places where local atmophperic pressure is 0.7 bar(a) or less and using bar doesn't help the math much.

David

RE: Do you want to switch to SI units?

Ornery:

Who's up for approximately four fifths of a pint of Guinness?

- Steve
 

RE: Do you want to switch to SI units?

3
If it's a question of what you like to use, it's what you are comfortable with. If it's a question of what's a better system then lets look at some comparisons.

Temperature:
C - 0 is the freezing point of water, 100 is the boiling point. Relatable and useful in many scientific and industrial settings.
F - 0 means...ahh...the coldest temperature they could achieve at the time. 100 means....ahh...the internal temperature of the human body...wait, we got that wrong.

Length:
m - Base 10. Enough said.
ft - 3'7-1/2" + 4'3-5/8" + 6'5-1/4" + 8'7" = need to convert into either inches or feet before I plug into my calculator.

Force:
N - Not as relatable as lbf unless you use them.
lbf - Not to be confused with lbm...or are they interchangable...and what about that slug thing? Do I need to multiply or divide by gravity to get to it?

Volume:
m^3 - yes, L are commonly used for liquid but you just need to move the decimal point around.
Oz - fluid volume (8 oz per cup), dry volume(wait...oz don't exists for dry volume). And don't forget weight (16 oz per pound). Don't like oz, ok gallons...wait US or Imperial. Don't like gallons, ok ft^3....now what's the conversion.

Scalability:
Metric - change the prefix, move the decimal.
Imperial - use a completely different unit of measure, find what wacky conversion is required and calculate.

RE: Do you want to switch to SI units?

Or you could just download something like 'Versaverter' (a free program found at:  http://www.pawprint.net/vv/ ).

I've been using 'Versaverter 1' since about 2000 and it works great.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

Yes - much easier to use and to computer program!!

When they built the new Federal Building here in St. Louis - all the dimensions were metric.  

Guess what - they had to go out and buy like $25,000 worth of dual marked tape measures for the Missouri farm boys building it.

Also, Canada is supposedly "metric" - but I get orders all the time for parts that 254 mm long (10'')  Go figure!!

RE: Do you want to switch to SI units?

Really, the ONLY advantage Imperial has over Metric, is that people are more familiar with it. If it was the other way around and Metric was here first and someone was trying to promote a switch to Imperial with all its odd conversions we wouldn't be having this conversation.

I am fairly young and I can't easily visualize metric (I need to do the math to give my weight/height in kg/m)...I do my calc's in metric and convert to imperial to get a feel for the size and forces involved in a problem...hopefully I will eventually develop a better feel for metric and forget about imperial.

RE: Do you want to switch to SI units?

MiketheEngineer,

   I am in a new building here in Canada.  The architects prepared their drawings in metric.  The actual construction drawings were converted to inches and feet.

   A lot of stuff is nominally sized in Imperial unts, but does not actually conform.  Lumber and pipe comes to mind.  You could just re-label these things in conforming metric units.  For example, 1/2"  pipe (Ø.840") can be called 14mm pipe.  

               JHG

RE: Do you want to switch to SI units?

   Oops.  When I typed "conforming metric units" I actually meant to type "non-conforming metric units", as a little arithmetic will reveal.

               JHG

RE: Do you want to switch to SI units?

Caneit, I'm fairly old and I cannot visualize metric, as well, and I use it more than imperial measurements for about the last 8 years.  

The imperial measurements are just old hat, as that what was ingrained so deeply into the grey matter in my youth.  They are not odd or quirky at all, if that's what one is programmed for and familiar with, like you said.

I have a WWI era Russian infantry rifle that has the rear sights graduated in Arshins.  It's very hard to gauge the target impact, especially after 4 or 5 kosushka's of cheap vodka!  Seriously though, I never drink at the rifle range.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

RE: Do you want to switch to SI units?

The interesting thing about this discussion is that anyone cares.  Any system of measurement is arbitrary.  If we say that a meter is so many multiples of the wave length of 6500K light or some such, it may feel "physical" but both the number of multiples and the light temperature are totally arbitrary.  Why do we keep getting exorcised over whose arbitrary number we use?  I often have a problem with people assuming that the system of units they use are universal and need not be communicated, but I've had that problem just as often with "Imperial" units as "metric" units.  It is all arbitrary and if I know the units I can do my job.  

I have a mish mash of "preferred" units in my head.  I have no problem thinking of pipe length in meters, but calling nominal 1-inch pipe 25.4 mm is tough.  MSCF is a pretty stupid unit, except that life is easier when you use it (the heat content of methane is about 1.0 MMBTU/MCF, much easier than 7900 kcal/SCM).  I can do psi or bar, but kPa and MPa might as well be Urdu.  I was looking at something with a design pressure of 10.2 MPa today and had to get UCONEER out to see if that was a big number or a small number.

I don't do kgf/m^2 at all.

David

RE: Do you want to switch to SI units?

we now have 43 replies on a self perpetuating thread.
Has anybody heard from ZeroExperience?
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

Quote (KENAT):


While it may get exaggerated as to how useful it is, many of the Imperial/US customary dimension are based approximately on body ratios.

   If only people were of a standard size.  Here in Toronto, Canada, I figure people are somewhere between five feet and six and a half feet tall.  People's body proportions are not that consistent either.  This rules out body proportions for any rational system of units.

   Part of the problem with the metric system in construction, is that people think in centimetres.  If they thought in millimetres, all the decimals and fractions would disappear.  Carpenters and welders would see a clear benefit to the metric system.   

   We all need to learn to stare blankly and stupidly at people who say "centimetres" to us.

               JHG

RE: Do you want to switch to SI units?

In a CAD system it makes sense to use something like a 'meter' as the base unit since that places the decimal place where you won't be wasting a lot of significant figureson the Left-hand side of the decimal place thus allowing for more precision on the Right.  This is why the actual database unit of measure for our major CAD products, NX and Solid Edge, both use meters, despite the fact that when using the software you're generally working in either Metric units (millimeters) or Imperial units (inches) but that's just a convention so as to make it easy to understand and to comply with normal design and manufacturing standards, but deep inside, all the numbers are stored as meters.  What this allows is being able to assure dimensional accuracy and precision down to the tightest manufacturing tolerances in general use today even for models so large as to just fitting into a cubic volume of space, one kilometer on a side.  

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

Fuel consumption calculations for a long haul jet would also get some clumsy numbers.

The advantage of metric is that in general it is real easy to adjust for magnitude by changing the prefix and moving a few decimal points.

The only real disadvantage is that a few units are non-intuitive (pascal for instance) and in some places they disturb the status quo.

To further improve, the counting system needs to changer from base 10 to base 8 or 16 for easy halving and re-halving. To bad for thirds as no matter what base that quickly becomes awkward with to the decimal repeated.

Regards
Pat
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RE: Do you want to switch to SI units?

But what would a system based on base 8 or 16 do for "moving a few decimal places"?

Now if our minds were taught to think like a computer we could just adopt a scheme based 2 raised to a power and be done with it winky smile

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

As an occasional adjunct professor, yes dear god yes.

As a practicing civil engineer, not only no, but hell no.


Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Do you want to switch to SI units?

The whole Imperial measurements being easier to visualise is rubbish. It's all about what you were brought up with.

All I have ever known is metric. As such, I visualise length in metres, mass in kg, pressure in kPa etc. Pounds, feet, psi, I have no idea what a unit of those looks like until I have converted it into its metric equivalent.  

RE: Do you want to switch to SI units?

Pat

"""Fuel consumption calculations for a long haul jet would also get some clumsy numbers."""

Some years ago they did that in Canada and turned a 757 into a glider.
B.E

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

They did to. I saw the show on TV, so it must be true.   

I also saw one where they had a leaky tank, so they kept transfering fuel from the good tank until they ran out. Can't remember whether they glided in or crashed

Regards
Pat
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RE: Do you want to switch to SI units?

Berkshire- That was the "Gimli Glider". They landed on an old airstip in Gimli, Manitoba. Luckily the copilot was a glider pilot in his spare time and He landed then plane after having no power for several miles. Mid ninties I think.

RE: Do you want to switch to SI units?

beej67....just out of curiosity, why the big difference in unit preference from teaching to practicing?  

RE: Do you want to switch to SI units?

Conversion could be confusing some. A spokesman from Southampton for Total, commenting on the current gas leak in the North Sea yesterday on CBC radio, estimated the gas leak at 50 cubic tons. I don't think he mentioned per hour or per day. Thank God time isn't going SI.

HAZOP at www.curryhydrocarbons.ca

RE: Do you want to switch to SI units?

50 cubic tons?

Not only is it total nonsense, the numbers don't even add up.

I read that it's leaking at an estimated 200000 cubic metres/day. Not sure what the reference pressure or temperature is, but assuming atmospheric, methane has a density of about 0.66 kg/m3, giving ~132 tonnes/day.
 

- Steve
 

RE: Do you want to switch to SI units?



Photographed by yours truly here in Toronto, showing how thoroughly we Canadians understand the metric system.

               JHG

RE: Do you want to switch to SI units?

Gimli glider is quite true.  The pilot asked for XXX amount of gallons but instead got XXX amounts of liters.  So he got about 26% of the fuel he requested.

Why he didn't believe his fuel gauges - God only knows - but us pilots are infallible.

And yes - they did glide it to an abandoned airstrip where a bunch of teenagers were staging impromptu drag races.  Fortunately, one of them saw the plane on short final and got everyone off the runway - just in time.  I believe he broke the nose wheel over running the end the rather short runway - it was designed for private aircraft.

Second story:

We have a manufactured piece - that is not critically precise (used in construction) but it was originally dimensioned in metric and fabricated in a "metric" country.  Then re-dimensioned in Imperial and built in US and this went back a forth for say a dozen years.  Guess what? The newer ones are about 1/4'' or 6mm different in length from the original because of all the transitioning of dimensions back and forth!!  Makes my life simple - NOT
 

RE: Do you want to switch to SI units?

And don't forget about that Mars mission that NASA lost a few years ago when one sub-contractor manufactured it's components based on the Metric system while the company that wrote the software that controlled it assumed that the specs they had been given were in Imperial units, what they had always worked in previously.  POP goes a few million in tax-payer dollars.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
UG/NX Museum:   http://www.plmworld.org/p/cm/ld/fid=209

To an Engineer, the glass is twice as big as it needs to be.
 

RE: Do you want to switch to SI units?

Thanks Steve for the gas leak estimate. I listened to the broadcast again and the speaker did not say per hour or per day, just 25-30 cubic tons. The speaker was Dr. Simon Boxall, an oceanographer and oil pollution expert. I don't think he was speaking on behalf of Total.

HAZOP at www.curryhydrocarbons.ca

RE: Do you want to switch to SI units?

We could always go back to the base 12 system of the Egyptians.

"On the human scale, the laws of Newtonian Physics are non-negotiable"

RE: Do you want to switch to SI units?

Well Total probably did not want to admit liability to an actual amount so he deliberately gave a nonsense figure that sounded like a real amount to the unwashed masses.

Regards
Pat
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RE: Do you want to switch to SI units?

Base 12 is a nice idea, but would require a revolution in basic microprocessor technology to make real, native use of it.

- Steve
 

RE: Do you want to switch to SI units?

What I find weird with Imperial, is the same unit is sometimes used for different measures. I am currenly looking at an old piperack drawing (chiseled out of stone, back when dinosaurs roamed the earth) and the steam line is denoted as 110 pound steam. So pounds for mass, force and pressure? Crazy talk.  

RE: Do you want to switch to SI units?

I did not know the Egyptians used a base 12 system. Live and learn, particularly on here.

You can still only halve twice before you get into fractions.

As to intuitive nature.

Generally but not always, metric is easier to remember and work with as units line up better and where mostly though through to be easy to work with when created, however nature does not always co-operate and things eventually get to a point where there is no option but to incorporate an awkward constant.

It is always more in intuitive to use the units we are most familiar with, hence my use of kph for driving my road car with a kph speedometer and kph speed limits. I learned to barefoot water ski and ski jump and slalom in the mph days, and I still call for mph from the boat driver as I know in mph how hard the water feels under my ski or foot.

With building standards, I still mostly think in imperial as the modules and tooling never changed. A 4 by 2 was still a 4 by 2, the name just changed to 100 by 50, but as it was still a 4 by 2 it stayed that way in the mind. 1/2" pipe is still 1/2" not 12.5mm and 4" pipe is still 4", but 90mm pipe is 90mm pipe as I never used an imperial version as a std size. Sure when I buy 4" pipe I know it might be called 100mm.

As for pressure, a force per unit area is a lot more intuitive than a straight up number that needs to be interpreted in the mind.

Regards
Pat
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RE: Do you want to switch to SI units?

   You people discussing number bases might appreciate this.

   I can't make out the publishing date, but it appears to be sometime in the 1880s.  You will have to zoom in a bit to read it.

   Nobody has mentioned the Sumerians, and base 60.

               JHG

RE: Do you want to switch to SI units?

Quote:

beej67....just out of curiosity, why the big difference in unit preference from teaching to practicing?  

SI is a billion times easier to teach, because your units almost always work out.  Pair that with the tendency in modern textbooks to represent any sort of flux as a little dot over the symbol of the quantity that's "fluxing," and it really makes a lot of sense.

All that sense goes out the window once you leave college and start dealing with the versions of the equations the old timers are using, and the design regulations are using.  

I hate teaching in anything other than SI, because SI is built from the ground up to make sense.  I hate engineering in anything other than imperial because imperial is what's been done before.   

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Do you want to switch to SI units?

I am eternally gratefully to my college adviser who also happened to teach most of the upper level courses I took. He forced us to solve all problems in units first, and he forced us to use imperial. It was a godsend to figure it all out then and have confidence in using the wacky and sometimes unintuitive units now. (People look at me blankly when I tell them they've forgotten their slinch's.)  

When the future's architectured
By a carnival of idiots on show
You'd better lie low

RE: Do you want to switch to SI units?

Hey drawoh, weren't these guys into feeling the lumps on your head in order to diagnose all sorts of physical disorders and mental weaknesses?  

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RE: Do you want to switch to SI units?

beej67,

"I hate teaching in anything other than SI, because SI is built from the ground up to make sense.  I hate engineering in anything other than imperial because imperial is what's been done before."

I guess that's where here (Australia) is different. I am not sure when metric ticked over here, 1960s I think, going by old drawings, but it is pretty rare to come across anything in Imperial units.

The worst I have to deal with is converting lengths and pipe sizes to metric. Usually that has already been done for me on updated revisions of old drawings though.

A 24NB pipe means nothing to me, but DN600, ah, I can see what that looks like in my head.  

RE: Do you want to switch to SI units?

The plane with the leaking fuel tank also glided safely to a landing in the Azores.  That too was a Canadian one.

I'm with those who think it has to do with what you're raised with, and what your typical labour force works in.  Despite being officially SI since I was a kid, Canada's tradesmen still work in feet and inches.  That the plywood is now 19mm instead of 3/4" etc. doesn't bother them a bit.

As to pipe sizes, they might as well be called George and Bob:  they are sized based on a table of ODs and wall thicknesses which have precious little to do with either their DN/PN or NPS "dimensions".

RE: Do you want to switch to SI units?

Quote (JohnRBaker):


Hey drawoh, weren't these guys into feeling the lumps on your head in order to diagnose all sorts of physical disorders and mental weaknesses?   

   Yes.  

   And they were into Octal.

               JHG

RE: Do you want to switch to SI units?

I'm sure if I lived and practiced overseas my whole life, and everything in the industry around me was in SI, I'd have zero reservations about SI.  

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RE: Do you want to switch to SI units?

I just ran into these conversion units the hard way this week.
I had a 3/4" gate valve strip out on a coldwater supply line.
  No problem I just go get the same make and model of valve, remove the top and install it, Right?   Wrong, the maker has moved his production to China. The new valve now has metric threads that do not fit. So I ended up dismantling by de- soldering a bunch of copper tubes and re-installing the new gate valve assembly into the line.
  A 5 minute job turned into a 2 hour job.
Don't you just love SI units.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

"Don't you just love SI units."

Yep. Like almost all of the modern World.

- Steve
 

RE: Do you want to switch to SI units?

Was the problem attributable to the new one being metric or the old one being imperial. If it was pipe fittings, more likely the old one being NTP and the new one being BSP

Regards
Pat
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RE: Do you want to switch to SI units?

Pat,
The old one was imperial 1-3/8" the new one was 30 mm. This is where the body of the valve screws together. The good news was that the pipe sizes were still the same .
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

I'd be careful with those pipe threads.  That 'metric' valve probably has BSPT threads which are almost the same as NPT threads, and with smaller sizes used for low-pressure liquid applications, you might get away with using them interchangeably.  But if it's high-pressure or gas or the pipe is larger than 2", don't even think of trying it.

The tooth angle for NPT is 60° while BSPT is 55°.  And there are differences in the thread-form as well.

For more information about this, go to:

http://pipeandhose.com/node/2

John R. Baker, P.E.
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RE: Do you want to switch to SI units?

Thats why I had to change the whole thing instead of swapping parts.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

Out of interest, how many people opining have actually used both systems 'in anger'?

I have to admit that while I've used Imperial/American customary more at work (at least linear measures & lbs), while almost all my education (except the aerospace design course taught by an American prof) was metric, in terms of hard core calculations most have been done in SI.

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RE: Do you want to switch to SI units?

My experience is sort of the opposite of yours, KENAT.  All education and first 15 years of work in US, then the rest in Australia.  There was a familiarisation period, and I still convert some things in my head, but I much prefer SI.

RE: Do you want to switch to SI units?

I was educated in imperial in Aus pre metric then about 5 to 10 years of mostly imperial in daily life before the transition was into full swing.

In school, all science was done in metric, but drafting was done in imperial.

I work on cars, and that always involved both as initially I worked on VW and GM cars, then GM cars came with mixed systems and I also started on Japanese cars which although metric are on some items, a slightly different metric to Europe.

I have done some machine work and built things. Using drills taps and dies gets interesting. Disadvantage is two complete sets of cutting tools, but the advantage is you are more likely to have the ideal size for a particular spot. For instance, 1/4" UNC is a bad size re thread strength and bolt strength at the root dia  but 6mm is better proportioned.

BSP vs NTP is more problematic as for some sizes great care has to be taken to differentiate, but a mismatch will assemble reasonably OK but will leak and be weak.

I have also used a lathe and mill where the calibrations are in imperial, but the drawing and micrometers are in metric. You learn to convert on the run and get a feel, but it is slow until you learn to think in an ambidextrous manner. It is always more prone to error.

Regards
Pat
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RE: Do you want to switch to SI units?

Kenat,
As you know I was raised in the UK and used imperial systems until the changeover. I also worked for an engineering company in the UK that exported systems to Russia. All of the drawings were drawn dual dimension and the tolerance stackups had to work in both sets of dimensions. There were little things like the banning of 1/4" bolts on the job, because we knew that the russians would stick a 6mm bolt in the hole if they lost one of ours and in some cases that smaller bolt would be marginal on strength.
 After I came to the States, I worked for a company repairing German fiberglass sailplanes. All of those dimensions were metric to DIN specs or LN so you were working mm, centimeters. or meters on american equipment calibrated in inches or thousanths therof.
Great fun.
 Now the latest, I just finished a package of drawings for a company (in inches) who sent them to a fabrication company who promptly asked if they could have them in metric. The good news there was that all I had to do, was change the units on my cad program. Then go back and check the tolerance stack ups.
B.E.
  

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

I was educated in metric units (although I was taught imperial at primary school).

In my time spent on the shop floor (alternator/starter manufacturing), the drawings were all in metric, but the machine operators all spoke in imperial, so it was very mixed. I could convert between microns and thou' without thinking for a while.

- Steve
 

RE: Do you want to switch to SI units?

This letter and a reply appeared in the PEGG (Alberta Engineering Association newspaper) in 2002. Sorry that it is a bit long, but I think it is interesting.(Authors names deleted).

Re: Earth's Warmth Tapped to Heat Aquatic Centre,
The PEGG, March 2002
Once again, I read a confused article with mixed units of measurement. From the article: "72,000 lineal feet of three-quarter-inch underground piping..."; "at 11 feet, nine feet and seven feet below the surface"; "moderate at about 7C from about two metres to nearly 300 metres"; "three 30-ton geothermal heat pumps."
First, mixing units in a single story is profoundly sloppy writing. Second, imperial measurements are utterly archaic and have absolutely no place in our official organ.

The purpose of this publication is to serve Alberta's engineering and geoscience communities, and these communities use SI. We have no need for any imperial measurements, and it is intolerable that the editorial staff insists on imposing imperial units on us because they are unwilling to expend a little effort to provide SI equivalents.

Ignorance of the metric system is pathetic and unacceptable. Canada switched over to SI in the 1970s. I'm afraid I cannot accept any argument against switching to SI; The PEGG and its editorial staff simply must catch up to the rest of the world.

I am embarrassed to imagine what professionals from other jurisdictions must think of Alberta's engineers from reading articles such as this.


Reply:

Re: Stop Mixing Measurement Systems, Readers' Forum, The PEGG, April 2002.

XXXX XXXXX, P.Eng., bashes mixing different systems of measurement and the very use of the imperial system. While he makes some valid points, I cannot accept his overly agitated tone and misplaced passion. This matter is certainly not as hot as he sees it.

The imperial system is archaic, yes; but it has served the mankind for centuries and for that alone, it deserves some respect. We are not the first nor the last people here; we are living in an environment created by previous generations, and these generations mostly used the imperial system.

To me, when dealing with existing facilities, 20 feet makes a lot more sense than 6,096 mm, 40 p.s.f. sounds more natural than 1.9 kPa; and when I drive on Icefields Parkway and see a sign saying that vehicles over 4,550 kg are prohibited on this road, I can't help laughing. Those who mindlessly converted 10,000 pounds to the metric system forgot that 10,000 is a round number, and is appropriate here, whereas after seeing the 4,550, one can only
ask: "How on earth did they manage to calculate it with such precision?"  It is just one of the myriad examples around us when common sense is sacrificed to a political campaign.

I was born and trained as engineer in Russia, and till age 33 I never knew what a foot and a pound was; still, it didn't make me a genius to figure that out when I started practicing in Canada. I often use mixed units in the same formula in my calculations, and it's OK as long as you are careful with the conversion factors. But the same holds true when you use any system of measurement; not to confuse meters with millimeters, kN/mm2 with MPa, and so on.

 And this problem is not unique to Canada. In early 1980s when the Soviet Union signed the SI convention, there was an attempt, in the weather forecasts, to call the atmospheric pressure in hectopascals. Guess what? In three months it was all rolled back to millimeters of mercury.

Custom and tradition are real factors, not to be taken lightly.
Mr. Moorman says that he "cannot accept any argument against switching to SI." Probably so; but who cares? Good designs, as well as bad designs, can be prepared using any system of measurement.

Finaly, any new graduate who hopes to compete in an international engineering marketplace knowing only one system of units is in for a rude awakening and a fast education.

XXXXX XXXXXXX P.Eng.
Edmonton
 

RE: Do you want to switch to SI units?

Without mixed use of units, we'd never have had the great line from The Young Ones, where cool Mike is chatting up a lady:

"I know what you're thinking baby and if I were to tell you, you'd think I was talking centimetres."

One problem with metric units is that 100 km/h isn't fast, 200 km/h is too fast. There's no equivalent of the "ton" that was so important to teenages on their bikes.

- Steve
 

RE: Do you want to switch to SI units?

KENAT,

   I learned English units in school, and eventually, metric.  In college, we worked in English and metric units.  The company I work for transitioned to metric when we adopted 3D CAD.

   I firmly believe that journalists should repeat the numbers and  units they are quoted.  I suppose an engineering magazine should be held to a higher standard, but conversions do lead to mistakes.  This is particularly true when the numbers and units are coming from some techie whose job you are not qualified to do.  No one here is a universal genius.   

               JHG

RE: Do you want to switch to SI units?

I worked in a marine exhaust shop that built custom stuff in inch units, for installation in yachts all over the world, with customers providing boat measurements or drawings in both systems.

We did a lot of scaling of drawings back and forth.  The worst problem I had was a fabricator/designer who infected a fair number of drawings with conversions using 25mm to the inch.

Before fabrication proceeded, we insisted on actual measurements of the boat, even if we'd been working with the plans, not because of any difficulty with conversions, but because the whole concept of interchangeable parts has not yet reached the boatbuilding industry.
 

Mike Halloran
Pembroke Pines, FL, USA

RE: Do you want to switch to SI units?

Same problem with building capital machinery.  Never trust the architectural drawings of the building where the equipment is going to be installed.  Send someone there with a steel tape and quadrille pad and don't start making your installation drawings until those 'as-builts' are setting next to you.

Not that it'll save you from stupidity, like the time AFTER we got the 'as-builts' the customer decided to upgrade his fire-sprinkler system without letting us know and when we went to erect one of the main peices of equipment (these machines were as large as a small house), we discovered that the new service mains entered the building and passed right through an upper corner of the steel framework.  Fortunately there were no moving parts in the area and all we needed to do was cope around the plumbing, but the customer got dinged for an extra day or two of labor and material costs.

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RE: Do you want to switch to SI units?

I remember back in 1977 when I was in  K-Mart store getting school supplies for my senior high school year.  At the time, I knew I was headed off to engineering school the next fall, so this conversation is one that I remember.

It was unseasonably cold, about 10 C or so.  The woman ahead of me was complaining to the cashier that it was the Canadian government's fault for implementing the metric system, since Celsius degrees are colder than Fahrenheit degrees.  (i.e., 10 vs 50).

So, by that line of reasoning, and with due regard to the increasing concerns over global warming, perhaps we all *should* convert to SI units, thereby saving the planet.

I should summarize this in a technical discussion paper to present to a managerial team of MBAs in order for us to move forward with this proposal.  

Regards,

SNORGY.

RE: Do you want to switch to SI units?

I agree with the woman, SNORGY.  I use Centigrade in the summer, Fahrenheit in the winter.

RE: Do you want to switch to SI units?

KENAT

I always thought the conversion factor between centigrade and Celsius was 1:1. Isn't it in fact just a language thing anyway. ie same word in different languages or is it something like hood vs bonnet or trunk vs boot.

Regards
Pat
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RE: Do you want to switch to SI units?

Thinking back to my physics days at school, I believe Centigrade is a 100 point linear scale between water's freezing and boiling points (or any two arbitrary temperatures), whereas Celsius was absolute and related to Kelvin by 273.15. Or something like that ... an A-Level question designed to catch out students.

- Steve
 

RE: Do you want to switch to SI units?

Yes the boring factoid is that the original Fahrenheit scale is a centigrade one, because he divided the difference in temperature between hot ox blood and some (rather good) freezing solution into 100 parts.

Cheers

Greg Locock


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RE: Do you want to switch to SI units?

And here I was told that the SI crowd was miffed because the Imperial scheme recognized the guy who invented it, Daniel Gabriel Fahrenheit, while their inventor's name was consigned to oblivion out of some pragmatic desire to give only descriptive designations to SI units and so they were stuck with Centigrade.  That is until some bright fellow pointed out that since they BOTH began with the letter 'C', that there was no reason that they couldn't quietly drop Centigrade and replace it with the name of the genius who first proposed dividing the range of freezing to boiling points of water by 100, Anders Celsius.

I kind of like my story better winky smile

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RE: Do you want to switch to SI units?

Greg,

It's coming back to me now. We had it drummed into us that centigrade was a type of scale, not a unit of temperature measurement.

- Steve
 

RE: Do you want to switch to SI units?

The Imperial measurement system has only been standardised since 1824 so serving us well for centuries is rubbish maybe 1 1/2. Before that nonstandard units created chaos.  

RE: Do you want to switch to SI units?

You know you're an engineer when discussing units of measure is a good pub topic...(for the record, I have this exact conversation with engineering friends over a beer. Needless to say, I think we sounded pretty attractive to any nearby females that overheard the conversation.)

RE: Do you want to switch to SI units?

Comming from an "old" metric (SI) country i can say "its just a unit system". Its like driving in the right side of the road. You are not aware of the fact that since China&India is driving in the left side  you will soon be a minority. This makes travel (to the countries where cars drive in the left side of the road) a little dangerous, but you will learn it fairly quickly if you need to.

Best regards

Morten

RE: Do you want to switch to SI units?

MortenA (Petroleum)
There you go, try going from London to Paris and back again 3 times in a week. Picking up a rental car in each city.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

RE: Do you want to switch to SI units?

MortenA,

   Is your "old metric" country mks (SI), or cgs?

               JHG

RE: Do you want to switch to SI units?

Don't let it get you down. Just take 1000 mg of vitamin C and try to relax.

HAZOP at www.curryhydrocarbons.ca

RE: Do you want to switch to SI units?

Tires are mixed 205/60-15.
205 is the width in mm
60 is an aspect ratio of width to sidewall height
15 is the rim/sheel mopunting diameter in inches

How this system has evolved into the mixed unit mess it is is beyond me. I know Society of Automotive Engineers standards have something to do with keeping it alive, but why not change the wheel to mm, 15" becomes 380mm. now you have 205/60-380 tire size.
 

"Wildfires are dangerous, hard to control, and economically catastrophic."

Ben Loosli

RE: Do you want to switch to SI units?

It's same reason why sparkplugs have always been metric even when the rest of an American automobile was in Imperial units back before that industry made the move to metric or why the hose connections on all fire hydrants and fire trucks around the world use a standard based on Imperial units.  Sometimes tradition, as in the case of Sparkplugs and Wheels, is the reason while in others, like fire hose connections, is the result of society being unwilling to take the chance that in an emergency a borrowed set of hoses will not be compatible with the local fire hydrants or the equipment available to fight a fire.

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RE: Do you want to switch to SI units?

Greg,

   It runs out that camera threads are 1/4-20BSW, and have been for something over a century.  1/4-20UNC screws work, but they were not available when the specification was worked out.

               JHG

RE: Do you want to switch to SI units?

Kenat....I have used both systems "in anger."

I'm from California, so I grew up on the US Customary system. I learned a little SI in junior high school science and quite a bit more in high school Chemistry (taught by my father) and Physics (taught by a brilliant man who was a scientist for the US Navy during WW2). Both classes used SI exclusively and both teachers insisted on units for all calculations.

In college (I graduated in 1980), Chemistry was 100% SI, Physics was about 60% US/40% SI, and my engineering classes were the other way around at about 60% US/40% SI. Some professors were sticklers for units, others (for some reason) were not.

Through education and work experience I am mostly conversant in SI, but by virtue of living in the US I am more comfortable with US Customary units. I can visualize some SI units, but certainly not all, while I can visualize almost all US units.

That being said, I would much prefer to work with SI units exclusively because they are internally consistent and easier to work with. However, because I use Mathcad quite a bit, I can mix and match units without having to worry so much about the fine points of converting units.

I was project manager or project engineer for the civil design for six federal projects: three federal prisons, two buildings at a naval air station, water system improvements at an Air Force base, and a fire protection pipeline at a Marine Corp base. I was also the project quality engineer for an infrastructure upgrade project at an existing federal prison. All of these projects were designed and drawn with SI units, but it wasn't all smooth sailing.  Two stories about this:

FIRST STORY

On the prison projects, the architect we were working for and his other consultants were fully SI capable, so the design process went smooth enough...well except for the dumbest drafter in our office who asked for my help because he didn't know how to draw a 4H:1V slope in metric (no joke). It's when the plans got to the field that problems began.

During the bid phase for the first prison project, I took a call from a confused contractor. He was having trouble with our storm drain design. The meat of the conversation went something like this:
Contractor: So, a 1200-mm pipe is a 48-inch, right?
Me: Yes.
Contractor: With a 5-inch wall [this was reinforced concrete pipe], that puts the top of the pipe 4.42 feet above the invert, right?
Me: Yes.
Contractor: But your invert at Pt#xxxx is 40.00 and the grading design shows a finished ground surface of 42.75. That puts the top of the pipe about 1'-8" above ground.
Me: No. All vertical information is in metric units. [I found most contractors haven't heard of SI, so I use "metric".]
Contractor: Whaddya mean the vertical information is in metric?
Me: The entire project uses metric units. Pipe cover at that location is about 1.4 m or 4.6 feet.
Contractor: Oh. So everything is in metric?
Me: Yes.
Contractor: Well, I'll be damned.

Next, the grading subcontractor's surveyor busted the US-SI conversion at the project benchmark. Actually, he did the conversion right, but he made a typo in his calcs that resulted in him being 1 foot off. I found out about this at the first partnering session when the contractor claimed there was about 200,000 CY of extra excavation than he had not planned on. As you can imagine, everyone from owner to architect to contractor was VERY worried. I wasn't because I knew our data and deesign were good, plus I suspected a US-SI conversion problem. I got permission to talk directly to the surveyor when I got home. The surveyor sent me his electronic files, including his ground topo map. By comparing about a dozen of his shots on existing concrete with our topo, I determined that the error was exactly 1.00 foot and not some random error. I then called the surveyor and told him what I had found and I asked him to walk me through his surveying set-up, including how he had handled the benchmark. That's when he spotted his error. He had (for example) noted a benchmark elevation of 152.35 feet, but his next calculation used 153.35 feet (a simple typo) for the conversion to SI. Ten minutes work and I looked like a hero.

During construction I had numerous small issues like this because both the contractor and the CM folks for the Bureau of Prisons insisted on working and thinking in US units.

SECOND STORY

The project at the naval air station only worked because my project engineer and I were competent with SI units. This was a design-build project. During the proposal phase, we sent our site layout designs to the architect so he could review them with the contractor. While I was out of the office, my project engineer got a frantic phone call from the architect, who said they were unable to scale our drawings. He said they couldn't match our dimensions with 10-scale, 20-scale, 30-scale, 40-scale, any architectural scale, or anything else he and the contractor were familiar with. The rest of the conversation went something like this:
Project Engineer: The drawings are in SI units.
Architect: Whaddaya mean they're in SI units?
Project Engineer: The drawings are in SI units.
Architect: WHY are the drawings in SI units?
Project Engineer: Because that's what the RFP requires and the survey the Navy the provided is in SI units.
Architec: But we don't have a metric scale.
Project Engineer: We got ours at OfficeMax.

Even so, we ended up winning the project. In the middle of the project kickoff meeting, the architect asked the Navy's project manager if SI units were still required or if the project could be done in "regular" units. The Navy's PM said "I don't like metric and my people don't either, so let's design this with "regular" units."

I raised my hand as said,
Me: As the civil engineer, I don't have a preference. However, the topo survey the Navy provided is in metric and I'm not willing to take on the liability of converting it to US units. Is the Navy willing to have the surveyor of recond convert the survey?
Navy PM: Why can't you convert the survey? We don't money in the budget to have the surveyor change the survey. [I found this hard to believe since the total project budget was $14M and the survey conversion could probably be done for several thousand dollars.]
Me: First, our firm does not do surveying. Second, converting the survey carries a liability I can assure you I will not get permission to take on.
Navy PM (in the best tradition of Solomon): Well, we can do the civil work in metric and the building can be designed in regular units. [no joke]
Me: Even though I think this is a bad idea, I know that my project engineer and I can make this work.

And we did, with no help from the architect. Fortunately, I was able to increase my project coordination task budget enough to cover the additional effort on our part.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Do you want to switch to SI units?

So, are you saying that the US cannot convert to SI units because the contractors, architects, and project managers are too stupid?  I've heard a lot of reasons, but never that one.

RE: Do you want to switch to SI units?

Not really. On all four federal prison projects I worked with the same architect; on two of the four we had the same prime contractor. Both are very large firms that do a lot of federal work and the people I dealt with were smart, flexible, and handled SI anywhere from competently to expertly. However, as a "practical matter" (I still wonder how practical), most of what the prime contractor and his subs did in the field was in US units, converted from the plans and specs (and much of what was in the plans in specs had originally been converted from US to SI by the design team). Some of the subcontractors were OK with SI, some weren't at all, and none were fully conversant with SI. I think only the contractor's surveyor worked completely in SI units, except for the starting benchmark.

Generally, the only time I saw the construction team using SI units was as the starting point for conversions to US units and in SOME of the submittals. Some submittals were preprinted brochures and if they weren't printed with SI (or at least US+SI), I wasn't going to get SI even if I asked "pretty please". Regardless, this wasn't a hill I wanted to die on. I had better luck with submittals for things like precast concrete vaults that used semi-custom drawings (i.e. standard drawings edits for our project).

The Bureau of Prison's CM staff had little enthusiasm for parcticing SI in the field. Most of them could handle SI competently, but the contractors were mostly using US in the field so the attitude seemed to be "why bother".

The architect for the buildings at the naval air station isn't dumb, but I don't think he's an intellectual heavyweight either. Regardless, both he and the DB contractor failed to completely read the RFP, which is something both and I my project engineer did. That's why they learned of the SI requirement from my project engineer.

This has little to do with intellegence (except the drafter...he's as dumb as a rock and I still can't figure out why my boss hired him...I had the guy figured out in less than a minute). This really has to do with comparative familiarity (US>SI), inertia (US>>SI), and the fact that most products being installed in this type of construction in the US comes in US units and not SI units (US>>SI). However, since SI>>>US, I think we as a country need to get serious about making the change and doing it as "cold turkey" as possible.

==========
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

RE: Do you want to switch to SI units?

Personally when working with materials in both units, I find it a lot easier in the field to convert to SI. A 4' wide sheet of plywood for instance might actually measure 1219mm, but a 1200 sheet might measure 47.24".

My tape will have 1219 marked on it but won't have 47.24. It will have 47 1/4 or 47 5/16 marked on it. It is easier to decide between 1220 and 1219 than it is to decide between 47 1/4 and 47 5/16 unless you have a tape marked in decimals of an inch. even so it's not practical to mark a tape in increments of less than 1/16th or 0.1" where it is practical and common to mark a tape in 1mm increments   

Regards
Pat
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RE: Do you want to switch to SI units?

Debating the benefits (or not) of inches over mm for construction purposes is completely missing the point. SI is a consistent system for engineering analysis across all domains, not a choice of length units.
 

- Steve
 

RE: Do you want to switch to SI units?

If SI is so great why has the world embraced kgf/cm^2 and bar as pressure units?  Could it be that kPa's are too small and MPa's are too big and there isn't a prefix for 10,000 times?  

Why do people who couldn't tell a "foot" from a "shoe" fluently talk about pipe diameter in inches and start counting on their fingers if they have to use DN numbers or mm?  

Why are road signs in the UK generally in miles and mph?

Consistent is good, but it falls apart if people can't or won't internalize it.

 

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Do you want to switch to SI units?

I think the man on the street argument fails horribly when you look at the pond. On the west side a 120 lb man is a shrimp, and on the other side a 26 stone man is an American. (sorry cheap jibe).

My point is that an order of magnitude (14) separates the 'natural' man on the street measures that at least bear some commonality.


  

Cheers

Greg Locock


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RE: Do you want to switch to SI units?

In my little professional bubble of engineering simulation, the only exception we have is rotational speed, which should be SI, but is more commonly rev/min.

Road signs in the UK are miles and mph by (stupid) law. A vehicle without an mph speedometer cannot be sold in the UK (!). I'm surprised our overlords in Brussels haven't outlawed all this.
 

- Steve
 

RE: Do you want to switch to SI units?

The guys doing engineering simulations of fluid mechanics tend to also use inches for pipe ID.  I see m, kPa, kg, C, kJ (but BTU is not unheard of), and inches.  I always chuckle when I see it.

I teach classes all over the world and get to see the range of units that people use up close and personally.  Every country (and many regions within countries) has their own way of reporting gas flow rates, and no one is comfortable in the other guy's units (no one outside of Alberta can automatically make sense of E3M3, and you have to be from Queensland to report a volume flow rate in MJ/day).  I teach in SCF after first getting an agreement that in any group of 10 engineers from 10 countries there will be at least 11 ways to represent volume flow rate (they all more or less understand SCF).  I can work in any of them, but more people get the concepts without the noise if I use SCF.  For pressures I use psi, but I use multiples of 14.5 psi=1 bar=100 kPa for the grid lines--it seems to work well.  For temperatures I use F, but set the increments in even multiples of C (this doesn't work as well because no one seems to be comfortable going back and forth in temperature).

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Do you want to switch to SI units?

David,

Our customers like to provide inputs and receive outputs in all sorts of wierd and wonderful units and we have systems to cope with that. Inside the actual simulation codes though, there's no place for furlongs or fathoms.

- Steve
 

RE: Do you want to switch to SI units?

I wouldn't be able to fathom such units furlong.

Sorry...

RE: Do you want to switch to SI units?

I guess that was a full toss. Well batted!

- Steve

RE: Do you want to switch to SI units?

Yep. Straight over the grandstand for six

Regards
Pat
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RE: Do you want to switch to SI units?

No one except me expresses acceleration in furlongs/fortnight^2, then?

RE: Do you want to switch to SI units?

I had my money on a horse that accelerated out of the box at a rate that would best be described in furlongs per year^2

Regards
Pat
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RE: Do you want to switch to SI units?

Back on road signs, I like the Aussie speed signs in some parking lots and residential areas that read 8 km/h... Cos thats easy to read exactly on a speedo

RE: Do you want to switch to SI units?

The 8kph is a direct hangover from 5mph speed limits.

I think no cars have a speedometer that is anywhere near accurate at less than 15 or 20 kph anyway, regardless of readability.

Regards
Pat
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RE: Do you want to switch to SI units?

""" I had my money on a horse that accelerated out of the box at a rate that would best be described in furlongs per year^2"""

Pat I think you are spelling it wrong, it should be "Furrowlongs" and it sounds like your horse should be pulling the plough. :)
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

RE: Do you want to switch to SI units?

Shortly after the start I certainly came to the conclusion it was more Clydesdale than Thoroughbred. This is of course a fictitious story for effect, just in case anyone thought it might be serious.

Regards
Pat
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