3 Replies Latest reply on Jul 25, 2011 11:22 AM by Mark Larson

# Rounding Number Option

Hello Everybody

Is there an option in 'Option' to round units dimension to the nearest multiple of 1/8 th?  Multiple of 1/8 means .13, .25 ,.38 , .50 ,.63,.75,.88 ,1.0...

All units must be in decimals, not fraction.  It would be a big help, because my boss wants me to change dimensions in all 8 pages of drawing!

Thanks

Do

• ###### Re: Rounding Number Option

Not in SWorks without some API custom routine.

This would introduce a fairly substantial error since some dimensions would round up and some down to the nearest 1/8". The resulting difference could be 1/8" error.

• ###### Re: Rounding Number Option

Rounding numbers is a great idea and actually necessary to be in compliance with certain requirements in several drafting standards.  What do you think about the following from SolidWorks Legion last year, and how would you like to see rounding of dimension values implemented in addition to current functionality?

### Rounding rule for dimensions

On most computer systems, decimal numbers that have 5 as the last digit are automatically rounded up when removing a decimal place.  For example, the number 1.425 rounds up to 1.43.  This creates a problem.  Most standards require that such numbers are rounded to the nearest even number in the last decimal place.  For example, that number 1.425 should be rounded to 1.42, and 1.435 should be rounded to 1.44.

ASTM E 29 states:

6.4.3 When the digit next beyond the last place to be retained is 5, and there are no digits beyond this 5, or only zeros, increase by 1 the digit in the last place retained if it is odd, leave the digit unchanged if it is even. Increase by 1 the digit in the last place retained, if there are digits beyond this 5.

NASA’s Engineering Drawing Standards Manual states:

When the first digit discarded is exactly 5, followed only by zeros, the last digit retained (i.e., the digit preceding the 5…) should be rounded upward if it is an odd number, but no adjustment made if it is an even number. For example, 4.365, when rounded to three significant digits, becomes 4.36. The number 4.355 would also round to the same value, 4.36, if rounded to three significant digits.  This procedure is known as odd-even rounding.

It is my understanding that this rule helps reduce statistical bias by allowing different numbers to be rounded up or down.  Using the computer default rule (5 is always rounded up) only allows for the upward rounding of such numbers.  This can create greater statistical errors, particularly when compounding rounded numbers to derive further rounded numbers.

### Rounding as it affects tolerances

No rule is absolute.  There are other considerations when rounding.  A number should never be rounded so that it increases the original limits of a dimension.  Although this rule mostly applies to inspection techniques, it can also apply to specification.  For example, if there is a feature whose size limits are 1.255-1.275, the specification cannot be rounded so its limits are 1.25-1.28.  In such a case where rounding occurs, the specification limits should be 1.26-1.27.  Fortunately, this isn’t something that often occurs in mechanical design (though it does pop up when trying to apply dual dimensions).

Usually, rounding the limits is something that more often happens in quality assurance during incoming inspection of products.  In such cases, Interpretation of Limits rule from ASME Y14.5 declares limits are absolute.  For example, 12.25 MAX is the same as 12.2500000000000000 MAX.  If the feature measurement is 12.2540, that measurement should not be rounded to 12.25, as it is still out of tolerance because it exceeded 12.25.

Right now, SolidWorks does offer one rounding option for dimensions.  In documents options, there is a setting to round numbers to the nearest fraction, but only if fractional numbers are in use.

Would you like to see a fractional rounding applied to decimal dimensions in addition to control over how a number ending in ".5" will be affected when the number of places after the decimal are reduced?

• ###### Re: Rounding Number Option

how about metric rounding applied to fractions???

IOW 1/4" becomes 6mm

an 1/8th of an inch becomes 3mm

1/32nd becomes 1mm

and 1/64th becomes .... nothing

no, I don't need it, but I'm sure somewhere, somebody's boss will