>Dear folks,
>
>I need your help with a few things, if you'd be so kind. Could anyone
>here provide me with the *official* references for the following: US and
>Canadian documents stating that imperial units are *defined* (pegged) as
>some metric value (especially the inch); when and why the decision was
>made by English speaking countries to "standardize" around the 25.4 mm
>value for the inch?
>
>And finally why prefixes cannot be considered conversion factors?
>
>The above request has been the result of a heated debate I've had with a
>local professor of chemistry who insisted that imperial units still have
>their own definitional standards. He also insisted that things like mm,
>cm, etc, DO need conversion factors, i.e. that 1 mm = 1/1000 x 1 m, etc
>(where the 1/1000 would be the "conversion factor" (SIC)). Despite my
>best efforts I couldn't get through to his head that my proposals were the
>truth, sigh...
>
>Thank you kindly for providing me with this info. You can answer to me by
>private e-mail if you wish. However, if you posted it to all it could
>avoid having a flood of people providing the same answer.
>
>Marcus
The British yard was measured against the metre and it was found that
1 imperial yard = 0.914 399 metre
or 1 imperial inch = 25.399.972 mm
The US yard was defined by the relation
1 US yard = 3600/3925 meter
or 1 US inch = 25.400 050 8 mm
I have not been able to find whether this definition dates from 1866 or 1893.
I believe that some time between the Great Wars, the International Standards
Association decided to use
1 inch = 25.4 mm
This compromise standard was adopted by the International Organization for
Standardization. It was adopted by Canada in 1950, and by a conference of
British Commonwealth nations and the United States in 1959. The US
Geodetic Survey will leave their surveys based on the old standard because
they are changing to the metric system.
I agree that the metric prefixes are conversion factors but they have the
special names of decimal multiples and submultiples.
It is true that each country has its own weights and measures law. I have
copies of the British and Canadian acts. They both define the imperial
units in terms of metric units. The United States has never been able to
legislate a weights and measures law, but metric units have been legal
since 1866, and the administration has defined conversion factors between
US customery measures and metric measures.
Joseph B.Reid
17 Glebe Road West
Toronto M5P 1C8 Tel. 416 486-6071
