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rounding off to 10mm

rounding off to 10mm

rounding off to 10mm

(OP)
Is there a way to round off numbers to the nearest 10mm?
As in 2776mm becomes 2780mm.

Second: while searching this forum for an answer to this, I found this (from 2007):

Quote (JohnRBaker):

When rounding, examine the figure following (i.e., to the right of) the figure that is to be last. This figure you are examining is the first figure to be dropped.

If it is less than 5, drop it and all the figures to the right of it.
If it is more than 5, increase by 1 the number to be rounded, that is, the preceeding figure.
If it is 5, round the number so that it will be EVEN.

The thread in question, however, does not make a reference to any standard on this. I'm interested to know if this is the same way for ISO.

Thanks.

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

(OP)
Damnit, this was supposed to go in the siemens NX forum. Well maybe the second question can be answered here.

Are there admins here who can move threads?

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

Just red flag your post here with an "oops" note to the admin.

Repost on the correct forum.

RE: rounding off to 10mm

There were no standards on rounding since 1946.
In general math, if it's 0,1,2.3.4 round down; if it's 5,6,7,8,9 round up.
 

RE: rounding off to 10mm

(OP)
@MJ good tip, but I'll just create a new thread there since question 2 fits better here anyway.

@CH that's how I was always thought to do it, but apparently NX does (or did in 2007, I should check it out) this differently, claiming it was according to ASME standards. Apparently it's a statistical thing. Full explanation can be found here:
http://www.eng-tips.com/viewthread.cfm?qid=197969

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

Thank you Walterke,

The "explanation" doesn't really explain anything.
How rounding 1.504 to 1.5 is different from rounding 1.514 to 1.5?
The person who came with this explanation probably didn't do well in school, if he is afraid of 0 being "not a real number".
Rounding off 0 is as legitimate as rounding off 1.

BTW, have you heard of "fourth" rule:
 "In rounding off numbers, if the first number dropped is 5, and all the numbers after the 5 is not zero, then the last number kept shall be increased by one. For example: 1.6501 = 1.7"

It looks like everyone makes them up as they please.
Also, the question still open: which standard? ASA Z25.1 – 1940?
 

RE: rounding off to 10mm

(OP)
It's not about the difference between 1.504 and 1.514.
It's the difference between 1.55 and 1.65. Both would be rounded off to 1.6 according to JRB's explanation. (so one rounded up and one rounded down, even if both have the same number to round off)

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

W,
I was talking about the "explanation" in the link you provided.
It was saying that rounding 1,2,3,4 down and 5,6,7,8,9 up creates un-even statistical results as if 0 didn't exist or it was not "the real number".
And, no, I am not buying into rounding to even numbers.
Also I don't understand concept of "rounding" applied to design. You round your experimental data. When you design you make part the way you want it. There is nothing to round.
 

RE: rounding off to 10mm

(OP)
@CH, this kind of rounding is also used in the financial world because when you add everything up at the end, you're statistically closer to the real number (and some numbers just HAVE to be rounded at some point).
I don't really see where he says that 0 is not a real number though...
All I can find is

Quote:

Remember that "rounding off" a zero does not change the value of the number being rounded off.

As for rounding in design, as soon as angles and circumferences are involved, you're pretty much bound to round something off eventually...

@KENAT, that's what I'm trying to find out :)

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

Well, exactly,

 "rounding off" a ONE does not change the value of the number being rounded off,  "rounding off" a TWO does not change the value of the number being rounded off.

But you know what? It is pointless discussion. I'd like to see actual standard first.

RE: rounding off to 10mm

(OP)
More a discussion on semantics then anything else if you ask me. So you're right, it's a pointless discussion.

And finding the standard is the goal I had when I posted this in this forum, since the people here seem to be more experienced on the subject.
Is there an ISO standard that says to round off differently?

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

I don't think ISO really needs it.
They do not have trailing zeros and they do not use number of decimals to indicate tolerance.
You can specify 12.3456 +/- 0.1 and be happy.
 

RE: rounding off to 10mm

Well, yes and no CheckerHater.  You can specify that but then you need a measurement system accurate to 5 decimal places to check it so it would still be frowned upon.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
 

RE: rounding off to 10mm

(OP)
You have a point, but I feel like, at times, it might cause confusion when 2 people round off in a different way. (since ISO doesn't describe how you SHOULD do it, either way is correct then?)

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

All I am saying is that dimensions and tolerances are representing fit form and function, not some lame attempt to legislate the mathematics.
And Walterke, if you are using metrics (judging from your example "2776mm becomes 2780mm") you cannot use number of decimals to represent tolerance in ASME as well.
It's 2776 +/- 10 if you have to. (gdallup, we can have measurement system measuring to whole millimeters, can we?)
 

RE: rounding off to 10mm

(OP)
I understand your point. The rounding off to 10mm wasn't a tolerance problem, it was just for aesthetics in a brochure (no important dimensions were harmed in the making of the brochure)

And yes, we have measurement systems that can measure whole millimeters :)

I'm still trying to come up with an example of how rounding off in different ways can cause problems later on but I can't seem to get anything formed properly.  

NX 7.5
Teamcenter 8

RE: rounding off to 10mm

I think the only real problem with rounding is converting inch to metric, or back – you have to make sure you didn't create larger tolerance, but you can always tighten you final result a little bit.

RE: rounding off to 10mm

Rounding off can cause all kinds of problems going from theoretically perfect model, to rounded of drawing because someone wants to invoke +-.01 from a 2 place decimal instead of +-.005 from a 3 place decimal etc. (your value may vary depending on what default tolerance values you're abusing).

It doesn't need to cause these problems (maybe there's the odd case but darn rare) but lazy/thoughtless/uneducated drawing producers often go in that direction.

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: rounding off to 10mm


OK, let's apply common garden-variety 6-th grade arithmetic to rounding.

Say, your drawing demands something like .XX+/-.03, .XXX+/-.003.

You model feature to .375. BTW, no one held gun to your head, you could make it .400.
You want it to be +/-.03, so you round it to .38, which results in limit dimensions .41/.35. (This is what machinist will check)
When you apply +-/.03 to .375 you get limits .405/.345.
Round them to same two-digit, you get .41/.35.

Same with even number.
Model .125. Round it to .13. Limits are .16/.10.
Apply +/-.03 to .125 you get limits .155/.095.
Round limits to two-digits and get .16/.10

As long as you stick to same rules you get same results. Not to mention that most of "rounding" problems are coming from designing in fractions and using number of decimals for tolerancing. Both belong in the museum.
 

RE: rounding off to 10mm

CH,

Quote:

"As long as you stick to same rules you get same results"
Wasn't it the reason why Walterke actually asked the question? Didn't he ask for the standard in order to see if there is an official ISO document forcing everyone to stick to the same rules while rounding off, always (at least in ISO world)?

And referring to your latest example - please look to the link.
http://www.hartnell.cc.ca.us/faculty/shovde/chem22s/roundingrules.htm
If you follow the rules from it you will not always get the same results like you are saying (example with .375). But even knowing this, the method from the link itself is not the key here. The key is that there are different round off methods, so different final results may occur due to that. Which one is correct and which is not is the other side of the story.

RE: rounding off to 10mm

Dear pmarc,
Can you please reference the standard that says this particular rule applies to how we round dimensions?
And when it comes to different ways to do the same thing; I suggest you research "Indiana Pi Bill". Just because something was approved unanimously, doesn't always make it right smile
 

RE: rounding off to 10mm

Dear CH,
Can you please reference the standard that says "your" rule applies to how we round dimensions?...

...I will repeat, there are different rules because there seems to be no standard clearly saying how to round off and in consequence making other rules illegal or at least not preferred in certain applications (i.e. technical drawings).

Please don't get me wrong. For your example I would round off in exactly the same way like you did, but not because of a standard, but because we were obviously taught the same during math classes. However even then I wouldn't say for sure that our standpoint was the only one absolutely correct. I am far from relying on wikipedia, but when you look to the following link you will easily see how many different rounding methods exist:
http://en.wikipedia.org/wiki/Rounding

I used the previous link just to show you that even for such a fundamental thing (I will never ever say "simple") someone may use different approach to ours and the final result of rounding operation will be different. And it is interesting that I found at least couple of websites supporting this method. All were not referring to any standard. It is even more interesting that the webistes standing behind our method did not mention anything about the standard too.  

RE: rounding off to 10mm


Pmarc,

I agree. Do you think it deserves further investigation? The standards mentioned in connection to rounding problem are numerous, but none of them actually addresses the issue directly.

Some examples are:
ASTM E 29 - 06 Standard Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications – operative words "test data", not exactly drawings.
 IEEE/ASTM SI 10 American National Standard for Metric Practice – named "primary" US metric standard the other standards should comply with. (I think I may be getting a copy)
Other "metric practice" standards like ANSI/IEEE 268 which is probably outdated by now.
ISO-31-0 apparently has "my" way of rounding somewhere in Appendix B Rule B.
None of them are drafting standards though.

The closest thing would be ASA Z25.1-1940 which is simply called "Rules for rounding off numerical values", but I've had no chance to see what's inside.

There are also lesser rules on the "urban legend" level, like "radius rule" – You round everything to even number because you may have to divide it by 2, like when calculating radius given the diameter.
"Ford ruler" – when Ford introduced decimal inches in 1932 the rulers were graduated in 1/50th of an inch because 1/100 would put too much strain on the eye. So second decimal must always be even, .38, not .37.

More input anyone?
 

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