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Engineering number formats
4

Engineering number formats

Engineering number formats

(OP)
How do you guys like your numbers to display when doing math?

Most of the numbers I work with are between 0 and a million.  So I end up with numbers like "589,484", or "12,587".  Ideally I'd like those to display with 2 or 3 sig figs, ie "590,000" or "12,500".  But there is no option to easily display numbers like this in any software I use.

The "engineering notation" option in MathCAD and other software doesn't work for me; it is hard to quickly read for most people.  589x10^3, 12.5E3 ... ugh.

Thoughts?

RE: Engineering number formats

Excel gives you some options. I use the ROUND function to pick the number of sig figs to display. ROUNDUP is also useful.

RE: Engineering number formats

(OP)
So you use round(...,-x) on your cells?  Thats a lot of work. =)

I want to see how other engineers like/would like to display and communicate numbers, and how many engineers use and like the "engineering notation" format.

RE: Engineering number formats

I generally perfer 'accuracy' over 'convenience'.

Now if you're teaching a class where you're trying to use simple, easy-to-understand examples which only need to be precise enough to get the point across, perhaps, but if I'm performing some sort of legitimate calculation and I get a complex result, I tend to use it as is and not try to imply any sort of 'tolerance' or 'safety factor' until I get to where I was headed since sometimes it not always that easy to discern early in a problem's workflow as to which parameters will be 'additive' or 'subtractive' with respect to the final result.  I would rather have a result I can have confidence in than one that might be easier to remember or manipulate when it's reused.  If that's an important consideration, I'd rather make that call ONCE and know that it's the ONLY accommodation which I've made in the entire process.

John R. Baker, P.E.
Product 'Evangelist'
Product Design Solutions
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
http://www.siemens.com/plm
http://www.plmworld.org/museum/

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

RE: Engineering number formats

Most of my numbers either come from or go into a computer program, usually via a file.  I like to use scientific notation with a fixed-width format so that the files are tidy (if there are multiple columns) and I have tight control over precision.
 

- Steve

RE: Engineering number formats

4
It drives me NUTS to see someone take a data point from a 2-inch 0-10000 psig pressure gauge as 119.547 psig when it is calibrated in 250 psig increments.  Then they take that into a +/-50% multi-phase flow correlation and predict the downstream pressure as 54.67899 psig.  What they really had was 125 psig (about half the first increment) and the downstream pressure is between 25 and 75 psig with the most likely answer around 50 psig, taking it to 5 decimal points is just nonsense.

Implying that "precision" in data reporting is somehow better "accuracy" is simply wrong.  When I was in school (the HP calculators were a couple of years old), I had a Mechanics of Materials teacher stand up and say that if the data would support an answer of 252 and your calculator read out as 252.1123, and you wrote that down with the decimals you were 100% wrong.  A lot of folks didn't take that to heart and after the first test most of those folks were gone.  He didn't care what numbers you wrote down on the intermediate calcs, but the answer had to be supported in the input data and the quality of the algorithms you used.  He was right then.  He would be right today.  We seem to have lost any comprehension of matching the answer to the input and it drives me crazy.

David

RE: Engineering number formats

@ zdas04:

I remember in my uni days we had a lecturer who was just as pedantic on the issue of "unjustifiable precision" as your mechanics lecturer.

I particularly remember he once set us an assignment to determine the water supply requirements for a city "with a population of 1 million people" - the important point being that one of your key input parameters had just 1 significant digit of accuracy. He would deduct 25% marks for every unjustifiable digit in your final answer. If your calculations arrived at a figure of 53.265 GL (say), the "correct" answer was 5 x 10^1 GL (or 5 x 10^10 L). Even writing 50 GL implied two digits of precision, and you would be down 25% straight away, while 53.3 GL would lose 50%, and so on.

While I am not as pedantic as he was, it was a lesson well learnt. In my own field of structural engineering, many of the design loads are probably only known to 1 or at best 1 1/2 digits of effective precision. (We may use a design wind speed of 47 m/s say, but do we REALLY know the wind speed with that level of accuracy, let alone the pressure coefficients on all surfaces of a building, and so on.) I let my calculations carry full computer / calculator precision, but I will generally format my final solution to show no more than 3 digits of precision (for which my lecturer would have knocked off 50% marks!)

Somehow, while deep in my gut, I know that we really only "know" the wind load effects etc to about 1 digit of precision, I have to report the rafter stresses as "125 MPa" say - I just can't bring myself to report the bending stresses as "1 x 10^2 MPa" or "2 x 10^2 MPa" for a rafter that is working quite hard.

RE: Engineering number formats

Surely 5 x 10^1 GL and 5 x 10^10 L are both wrong on the basis of not using engineering standard form? Leaving the reader to have to convert it into standard form to be able to say "fifty giga litres" instead of "five times ten to the tenth litres"

Will
Sheffield UK
Designer of machine tools - user of modified screws

RE: Engineering number formats

I'm a bit younger than zdas, but when I went to school we were taught the importance of significant digits.
johnbaker is right.  What we were taught was to carry the digits on through the calculation (when necessary) so that problematic rounding errors would be avoided.
I still dismiss anyone's information as ill informed if it is reported in too precise a number.  It is a sure sign of ignorance.

RE: Engineering number formats

(OP)
Hmm so none of you appear to use "engineering notation" (not to be confused with "scientific notation"), except maybe Ninja182.  Is it more of a metric thing, and not so common in the US?

Surely there are some other engineers out there that like to make things as simple as possible when communicating numbers.  

If I tell someone "120,000lbs", there is little room for misinterpretation.
"1.2x10^5" will get a "huh?" from the average person.
"120x10^3" not much better.
"118,427" looks unprofessional imo, and for lack of a better word, bore people. =)
"60 tons" is ambiguous.
"120k", "120kip" isn't always understood.

Yall see where I'm going with this range of numbers?

/not a very good geek.  :D

 

RE: Engineering number formats

Measure with a micrometer, mark it with a crayon, and cut it with an axe.

Accuracy needs to fit the task.

RE: Engineering number formats

I agree with David's point.  We had some kind of lab class on measurement accuracy and the Prof made the mistake of telling us during a lecture session that (would have been bourdon tube) gauge accuracy was +/- one half of the least count.  After that that is all we ever wanted to put as the accuracy instead on our lab results of what ever method he was trying to teach and he lamented that he regretted ever telling us that.

Therefore David, the gauge you mentioned if I looked at it would have an accuracy of +/- half of 250 = 125 which makes a reading of 119.547 outside the minimum accuracy of the gauge.

I have used the rule of thumb all of my career when I read any gauge.

rmw

RE: Engineering number formats

And then there is paralax.  Basically you can get any damn number you want off or a bourdon gauge.  I was in a meeting of about 50 compressor mechanics once and held up a test gauge and said "I'll give this gauge to anyone who can tell me what the mirror is".  I kept the gauge.  Every one of these guys had a high-precision test gauge (with the mirror) on their trucks, none of them knew why.

If you don't know what the mirror is for (and care) it is:

Quote:

When you position your head such that you can't see the reflection of the needle, you are reading the right value

David

RE: Engineering number formats

Duh, thought everybody knew that.

RE: Engineering number formats

TerryR1,

   I was taught about engineering notation in college in Canada back in the '70s.  I like it a lot, and I wish spreadsheets and programming languages supported it.  

   I have written a C subroutine that outputs numbers in engineering notation.  

               JHG

RE: Engineering number formats

A surveyor, engineer, CAD drafter, mathematician and a lawyer are all in a room and are asked "What is the answer to 2 + 2".

The surveyor says "4.0", because he only believes his level rod to the nearest tenth.

The engineer says "4.00", because he only believes any answer to 3 significant figures at most.

The CAD drafter says "3-63/64"...

The mathematician says "4".

The lawyer says "What do you want the answer to be?"

RE: Engineering number formats

The mathematician disappears for weeks.  He returns, having not eaten or washed and pronounces: "There is a unique solution!"

- Steve

RE: Engineering number formats

   I thought it was accountants who ask you what you want the answer to be!

               JHG

RE: Engineering number formats

Accountants make sure it comes out as 1, but 4 times in different places.

Will
Sheffield UK
Designer of machine tools - user of modified screws

RE: Engineering number formats

The accountant thing isn't funny.  I work as a framer for a general contractor who used to be an accountant.  He thinks everything should resolve and stud walls should be within a sixteenth.
Accountants should be barred by law from practicing anything but accounting.
I have no idea how this guy has managed to stay in business, but all his contracts are for high dollar cost plus jobs and he has so far apparently been able to get away with the insanity.

RE: Engineering number formats

I'd recommend just not getting hung up with sig figs. In my work, there are often many people working on a problems over a pretty long period of time. Accuracy should be 3+ sig figs, but if only 3 were reported at each point, the result would be an unnecessary and undesirable loss of accuracy. Personally, it doesn't really bother me to see a result reported as (say) 12,315, though I will cringe if it's instead reported as 12,314.876. I like to carry about 2 more sig figs than I think is truly justified, dropping down to the more correct accuracy only for a final result. I think people reporting excessive sig figs are not really thinking about the significance of those extra digits. We live in a world where most of our answers are coming from computers which will gladly display as many digits as we care to see.

RE: Engineering number formats

Years ago, at university, we did a slope stability calculation - by hand.  The scale was 1"=40'.  We had to use an engineer's scale to "size" the slice (you all remember what an engineer's scale is, eh? - many of the young Indian and Indonesian engineers I've met don't) - anyway - he determined the weight of the slice to the nearest 0.01 pounds!  I asked him what would happen to the safety factor if a dog took a dump.  

I like to try to keep things to sigfigs or at least something reasonable.  A lot has been lost with the advent of computers and calculators - slide rule precision baby - that's what it is about in my type of engineering . . . especially when "stuff" like unit weights are guesstimated (and sometimes badly).

RE: Engineering number formats

I have my calculator set for engineering units fixed at for 3 decimal places either above or below 1.  So .123 is 123.000e-3 and 1,000 is 1.000e3.  Reason being I work both in the many inches/feet and also on the mills of an inch.

Tobalcane
"If you avoid failure, you also avoid success."
"Luck is where preparation meets opportunity"  

RE: Engineering number formats

Besides irritating a few purists, I see no disadvantage to seeing excessive significant figures. Have you ever heard of a design failure because someone actully believed that an unreasonable level of accuracy was attained and did a critical design based on that level of accuracy? I've never heard of such a situation and so would claim "no harm" to overzealous reporting of sig-figs. On the other hand, real harm can result from excessive rounding or under-reporting of sig-figs. So if I were to be bugged by someone claiming I report excessive figures, I'd tell them to get over it.

RE: Engineering number formats

djack,
If I saw one of your reports that implied 9 digit accuracy I would get out my magnifying glass to see where else you were lying to me.  Sorry to be blunt, but the the output of a +/-10% calculation with inputs that are no better than +/-5% is not 123.456789012, it is "about 125", or "in the range of 100-150".  I have never seen a report where an engineer reported unreasonable precision that he didn't also have other errors that were material.  Every time.  People who don't bother to consider the precision of their inputs and equations tend to also be sloppy engineers who put too much reliance on what the computer tells them, often without bothering to verify that equations they are using are even germane to the problem they are trying to solve.

You are right that you would rarely have a case where you would make a different decision with and answer of 123.456789012 or 125, but my issue is that while 125 might be defensible in the data, the other number isn't.  Ever.  I suppose that makes me a "purist".  So be it.

For intermediate steps I always use the full precision available.  Rounding the intermediate steps does not add value (we did it in the slide rule days, but they're gone).  When you get to the end, an engineer is obligated to look at the result and assess his confidence in it.  I do that by tossing implied, unsupported precision.

David
  

RE: Engineering number formats

David, I too spent many years with a yellow steel Pickett slide rule as my primary calculating machine. I'll grant that feeling confident with as few as 3 sig figs is sometimes a stretch when using a slide rule. And, there's lots to be said for having a "feel for the numbers" when you need to maintain the decimal point in your head. But I'll still maintain that if you do a calculation and report the answer as 125, and I do the same calc and report 123.456 (let's not get too carried away), and if we theorize that it would be possible to could go back and attain greater accuracy with more precise measurements, than I am at least as likely to be closer to the "real correct number" as you are. And isn't the whole point to doing a calculation, to get the "right" answer?

RE: Engineering number formats

Djack,
Absolutely.  My problem is the squishy definition of "right".  In the world I live in (mostly fluid mechanics stuff) there are very few closed-form solutions to problems, and the few that exist were developed based on a page or two of assumptions.  Consequently, I rarely do or see equations that support much better than +/-10% (and most of them are closer to +/-30%).  So if I take the most precise data that the human mind can devise a tool to capture and feed it into an equation where I'm basically pulling a result off of a poor Xerox of a 9 scale log-log chart, then I get uneasy saying 125 instead of "over a hundred".  I couldn't bring myself to say 123.456.  I'll carry 9 decimals in the intermediate steps (my Picket is in a box as well), but I'll make the answer reflect my confidence in the data.

If I had a problem with a closed form, general equation that didn't have to contain any assumptions, then if I had great data I'd take the answer to the precision that was supported by the data.  I just never have that.

David

RE: Engineering number formats

I find it disturbing to see conversions from US to metric when the US version is "10 miles" and then the writer incloses in parentheses "16.1 km" when the narrative clearly indicated the "ten miles" was "give or take" and now we have a metric equivalent with an implied accuracy of a hundred meters.

Or vice versa.

old field guy

RE: Engineering number formats

oldfieldguy,
That is the perfect example.  Multiply a constant times an approximate value and change the uncertainty from +/-0.5 miles (804.672 m) to +/-50 m (164.042 ft).  

10.0 miles could easily be called 16.1 km since then the uncertaingy is +/- 0.05 miles (80 m) and +/-50 m which are certaintly in the same ball park.  

It is not hard, but it seems to be a lost concept.

David

RE: Engineering number formats

David--

Exactly.  Especially when the figure is written by a reporter who wouldn't know a "significant digit" if it bit him in the ass...

old field guy

RE: Engineering number formats

It's clearly time to metricate the US, and thus solve the problem for all eternity. Or at least it would until you guys invented a US litre (spelled liter, or course) which measures 0.9 litres. tongue
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Engineering number formats

Yeah, metric is wonderful.  I especially like kgf/cm^2 for pressure.  I enjoyed the speed limit signs on the roads in London expressed in mph.  Ask a girl in the UK how tall she is and she'll usually say ___ ft ___ in (sometimes it'll be in cm, but in my experience people convert from our irrational system), ask her weight and she'll say 7 stone 7 [lb].  Yep, metric solves all the communication problems.

David

RE: Engineering number formats

Yeah, we're a mongrel nation. I'm guilty of all of those examples - although I can't claim to be 7 stone lol - but I use SI units in my professional capacity.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: Engineering number formats

I wish I had taken a picture... a good many years ago, I saw a highway sign that stated: "CONSTRUCTION NEXT 7.537 MILES"
blllttt

RE: Engineering number formats

That is outrageous, but if it had said "7 miles 2835 ft" you wouldn't have noticed (maybe you would have, but most people wouldn't).

David

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