Chris Albertson wrote:
On Tue, Jun 25, 2013 at 9:17 AM, Bob Stewart<b...@evoria.net> 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?
Some years ago in 1959 the inch was re-defined to be exactly 25.4 mm.
Before that time the inch was only very close to 24.5 mm But for the last
50+ years 24.5 has been an exact conversion.
Likely people who are now 65+ years old where taught something different in
school if they were in school befoe 1959 and did not keep up with this.
To make it even more interesting there were several "flavours" (US,
Canadian, UK ...)of the inch which all differed by a very small amount.
Bruce
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