"David R. Birch" wrote in message
...
My company occasionally receives customer CAD files that have all or
most dimensions in inch fractions. What puzzles me is that when I
convert the fractions to decimal inches, the actual values turn out
to be only approximations of the fractions.
...
Why does this happen? How do you input 1/8" and get something other
than .125"?

David

It may be an accumulation of rounding errors. I've had to manually
reconstruct the intended location of features dimensioned as two-place
decimals obviously converted from fractions, 0.62" for instance, and
make sure the sum of dimensions equalled the (ref) length of the part.
That was trial-and-error detective work.

A friend at Saco did that for the 50 cal machine gun that John
Browning originally dimensioned to 1/128".

It's helped to learn the fractional and metric conversions, so I
recognize that the 0.434" I measured on an old South Bend part the
other day was 7/16" minus a production tolerance, or 0.that 470" means
12mm.

jsw