Hi Bob,
On 06/25/2013 06:17 PM, Bob Stewart wrote:
Hi Hal,
I had always used 25.4001 or .03937 to do my conversions. So, I looked online and found
the .039370078 and did the reciprocal. It is, indeed very very close to 25.4. If you
google "25.4001 conversion" you can find lots of tables using that as the
conversion factor online. I don't know where the error came from or why it's quoted so
regularly. But, it appears to be the rounded result of taking the reciprocal of a
rounded number. Don't machinists use this number for conversion?
Thanks for the discussion, everyone.
US Metric Act from 1866:
www.nist.gov/pml/wmd/metric/upload/HR-596-Metric-Law-1866.pdf
http://lamar.colostate.edu/~hillger/laws/metric-act.html
In 1912 C.E. Johansson decided to use 25.4 mm for one inch (at 20
degrees C), for his gauge-sets. That was later agreed internationallly
on in 1933, but the US Metric Act remained unchanged, which caused
confusion ever since.
Interesting article:
http://www.changeover.com/metrology.html
Anyway, unless you need to use a US Survey feet, 1 inch = 25.4 mm
exactly is what you should be using.
Cheers,
Magnus
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