The inch was not set at 25.4 millimeters centuries ago, but in the
1950s. Attached is an RTF copy of a 1975 Federal Register Notice issued by
the National Bureau of Standards clarifying the difference between the
International Foot (which produces the relation that equals 25.4
millimeters to an inch) and the U.S. Survey Foot.
Jim McCracken
At 12:18 PM 7/31/02 +0100, Markus Kuhn wrote:
>It just occured to me, had the inch been chosen to be 25.6 mm instead of
>25.4 mm, then all commonly used binary inch fractions would have been
>multiples of 0.1 mm, something that no doubt would have significantly
>simplified metrication in many industries.
>
>1/2 in = 12.8 mm, 1/4 in = 6.4 mm, 1/8 in = 3.2 mm, 1/16 in = 1.6 mm, etc.
>
>Just a thought, unfortunately two centuries too late ... :(
>
>Markus
>
>--
>Markus G. Kuhn, Computer Laboratory, University of Cambridge, UK
>Email: mkuhn at acm.org, WWW: <http://www.cl.cam.ac.uk/~mgk25/>
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}{\info{\title Appendix 9}{\author Linda Crown}{\operator Jim McCracken}
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{\plain \f1\fs26 DEPARTMENT OF COMMERCE\par
}{\plain \f1\fs26 National Bureau of Standards\par
}{\plain \f1\fs26 \par
}{\plain \f1\fs26 CUSTOMARY SYSTEM OF WEIGHTS AND MEASURES\par
}{\plain \f1\fs26 \par
}{\plain \f1\fs26 Commercial Weights and Measures Units}{\plain \par
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{\plain \fs20 In the FEDERAL REGISTER of July 27, 1968 (33 FR
10755), the National Bureau of Standards, in
accordance with a recommendation of the House
Committee on Science and Astronautics and pursuant
to the responsibility of the National Bureau of
Standards for "the custody, maintenance, and
development of the national standards of measurement"
(15 U.S.C. 272), published a listing of the common
weights and measures used in normal commerce
throughout the United States, and related them to the
standards developed in accordance with existing law. In
connection with the notice of July 27, 1968, the
following explanatory material will assist in the proper
interpretation and application of the data in column
three under "Linear Measurement, U.S. Customary,"
and under "Area Measurement, U.S. Customary":\par
}{\plain \fs20 As the July 27, 1968 notice states, all U.S. Customary
Units of linear and area measurement that will be found
in ordinary commerce are derived from the yard. The
yard \\vas last defined in a notice in the FEDERAL
REGISTER of July 1, 1959 (24 FR 5348), as being
exactly equal to 0.9144 meter.\par
}{\plain \fs20 The foot defined by the equations:\par
}{\plain \fs20 \par
}\pard
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{\plain \fs20 3 feet =1 yard = 0.9144 meter, exactly\par
}{\plain \fs20 1 foot = 0.3048 meter, exactly\par
}\pard
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{\plain \fs20 \par
}{\plain \fs20 is known as the International Foot. In addition, the July
1, 1959 notice defines the U.S. Survey Foot as follows:\par
}\pard
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{\plain \fs20 \par
}{\plain \fs20 1 survey foot = {\field{\*\fldinst ADVANCE \\u 5}{\fldrslt
}}1200{\field{\*\fldinst ADVANCE \\d 3}{\fldrslt }} meter, exactly\par
}{\field{\*\fldinst ADVANCE \\u 3}{\fldrslt }}{\plain \fs20 3937\par
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{\plain \fs20 or\par
}{\plain \fs20 \par
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{\plain \fs20 1 survey foot = 0.304\~800\~61 meter, approximately\par
}\pard
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{\plain \fs20 \par
}{\plain \fs20 \pard\column Accordingly, it is necessary to differentiate between the
international foot, used for engineering, and the U.S.
survey foot, used for mapping and land measurement.
The metric equivalents listed in the July 27, 1968 notice
for land measurements. statute mile (U.S. survey mile),
acre, square mile, section, and township are
approximate; metric equivalents to more figures can be
determined from the survey foot. For example, the U.S.
survey mile equals 1.609\~347 kilometers,
approximately, whereas the international mile equals
1.609\~344 kilometers, exactly. Metric equivalents of all
surveyor\'92s units, e.g., links, rods, and chains, are
derived from the survey foot.\par
}{\plain \fs20 The relationship\par
}{\plain \fs20 \par
}{\plain \fs20 1 international nautical mile = 1.852 kilometers\par
}{\plain \fs20 \par
}{\plain \fs20 is exact, but the relationship\par
}{\plain \fs20 \par
}{\plain \fs20 6076.115 international feet = 1 international nautical
mile is not exact.\par
}{\plain \fs20 \par
}{\plain \fs20 Dated. January 17,1975.\par
}{\plain \fs20 \par
}\pard
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{\plain \fs20 RICHARD W. ROBERTS,\par
}\pard
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{\plain \fs20 Director.\par
}\pard
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{\plain \fs20 \par
}{\plain \fs20 NOTE.- This document is republished from the issue
ofJanuary 22, 1975 ( 40 FR 3486).\par
}\pard
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{\plain \fs20 [FR Doc. 75-2011 Filed 1-21-75; 845 am]\par
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{\plain \fs20 FEDERAL REGISTER, VOL, 40, NO. 23-MONDAY, FEBRUARY 3, 1975\pard
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