Markus Kuhn asked in USMA 21452:
>Jim McCracken wrote on 2002-07-31 13:45 UTC:
>> The inch was not set at 25.4 millimeters centuries ago, but in the
>> 1950s.
>
>Was setting the inch to 25.6 mm or 25.0 mm seriously discussed as an
>option at this or at any earlier opportunity? Is the rationale for the
>choice of 25.4 mm for the inch documented somewhere in more details, as
>well as the history of previous definitions for the inch?
>
>When was the inch defined in the US for the first time with an accuracy
>of better then 0.1 mm? the practice of length measurement with a
>relative error below 1% surely must predate the 1950s significantly ...
>even centuries ...
>
>Markus
The imperial yard was measured against the metre in 1897 and found to be
1 yard = 0,914 399 metre, or 1 inch = 25,399 972 mm
The American yard was defined in the Mendenhall Order in 1893 by
1 yard = 3600/3937 meter, or 1 inch = 25,400 050 8 mm.
The International Organization for Standardization (and perhaps the
preceding International Standardizing Asspciatioin) adopted an
international inch of 25.4 mm.
Canada in 1950? decided to adopt the ISO inch.
In 1959 a conference of English-speaking countries adopted the ISO inch of
25.4 mm.
Joseph B.Reid
17 Glebe Road West
Toronto M5P 1C8 Tel. 416 486-6071
