Educate me... Dimensioning Accuracy. Decimal vs Fractions

[rodalsa]

I stumbled upon the dimensional differences shown on the attached DeltaCad file.   I generated this file by first selecting either the 0.0001 or the 3 1/32 measurement units while measuring the various dimensions of object.  These dimensions are noted by the underline in red.  I then converted the DeltaCad output to its opposite units (0.0001 or 3 1/32).

My question is this:  When seeking the most accurate measured dimensions which of the two units (or other units) will give me the best answers?

A follow on question is:  Is there a description or code segment say in Visual Basic that would allow me to understand the round offs that must be used when translating from decimal to fractions?

[jw48]

Hello Rodger


I tried a similar thing but couldn't reproduce the problem you describe. Perhaps I'm misunderstanding something.


  Dimensioning oddity 2.dc (Size: 952 bytes / Downloads: 5)

If I use [Dimension | 3 1/32] I get   1 19/32   as you do.  If I use [Dimension | 0.00001] I get   1.59375  which is correct. If I use [Dimension | 0.0001] I get   1.5938   which is the correctly rounded-up dimension.  I haven't seen 1.6000 at all, whatever I try - could you explain how you got this figure?

Which version of Deltacad are you using?

Your follow-on question is outside my experience, I'm afraid.

John

[AlwMVMO]

Deltacad stores it's geometry in the database as a decimal to an accuracy of .000001 no matter what the value that is displayed.

The smallest fraction available is ( 1/64 ) which is .015625, is 15625 times greater than the decimal accuracy.
The fractional values are for display only for people who are designing and making projects using tape measures.
I have never seen a decimal value in a fractions before ( 19.2/32 ), it's always been whole numbers on the top and bottom ( 19/32 ).

P.S. 
I see Deltacad version 3.1 only goes to .0001 accuracy or 1/16 and version 8.0 goes to .000001 or 1/64

[jw48]

As I understand Rodalsa, he inserted e.g. 19.2/32 manually, to illustrate his point.

Anyway, the whole problem only rears its head when you use cheap Chinese rulers.

[AlwMVMO]

For your second question:
All fractions have a decimal values. So you need to compare the decimal value of the fraction to the decimal number to find the closet fraction.
But only use fractions with denominators with 2, 4, 8, 16, 32, 64

example:
1/2 = .5
3/4 = .75
5/8 = .625
9/16 = .5625
19/32 = .59375
39/64 = .609375

There is a conversion chart under the Definitions, Charts and Formulas forum at:
http://deltacadusersgroup.org/Forums/showthread.php?tid=568&pid=1857#pid1857