John Nichols wrote in USMA 233344:
The inch as I understand is defined as 25.4 mm exactly. By Congress in 1877?
Congress legalized the use of metric units for all purposes by bill H.R. 596 in 1866. President Harrison received copies of the prototype metre and kilogram in 1890. Thomas C. Mendenhall of the Treasury in 1893 issued a bulletin declaring these prototypes to be the "fundamental" U.S. standards of length and mass. I believe he also declared the yard to be 3600/3936 metre (0.914 401 828 m). The British yard was measured and found to be 0.914 399 m. ISO, and probably ISA before it decided to use a yard of 0.9144 m. Canada adopted the yard of 0.9144 m in 1951. In 1959 (I think) a conference of English-speaking countries decided to adopt this yard of 0.9144 m. The U.S. Geodetic Survey announced that it would not change it records because it was changing to the metric system. The old U.S. foot is now known as the survey foot.
As I tell my class the US inch is a metric defined by the US Congress, but it is not an SI unit. If they wish to measure in units of 25.4 mm go ahead. To determine an statisitical inch one first has to establish the metre divide it into 10000 parts and 254 of them are an inch.
The U.S. Congress has never defined any weights or measures, although it has come close to doing so on several occasions.
Joseph B. Reid
17 Glebe Road West
Toronto M5P 1C8 Telephone 416-486-6071
