I don't see any mention at all here that the United States adopted the metric system officially as legal for all purposes in 1866.[1] Because this was by act of

I don't see any mention at all here that the United States adopted the metric system officially as legal for all purposes in 1866.[1] Because this was by act of Congress, the Supremacy Clause in the Constitution means that all state governments have to fall in line and permit the use of metric measurements--and they do. It is custom alone that has slowed the thoroughgoing adoption of the metric system in the United States. Lots of subsets of private industry have been mostly metric for many years,[2] so we are talking about activities at the margin of international trade and science and other activities in the United States that have long been increasingly metric. I have lived in Taiwan for six years of my adult life (two three-year stays) and I have become used to thinking metric about overland distances in kilometers or my own height in centimeters or temperatures in Celsius degrees. But over there too, customary units survive long after official metrification, although some of those (like the unit of weight 斤, usually translated into English as "catty") have been conformed to the metric system by being defined in metric units (so that now a catty is half a kilogram). This process may go on for a long time in the United States. [1] http://www.unc.edu/~rowlett/units/usmetric.html http://www.unc.edu/~rowlett/units/usmetric.html http://www.law.cornell.edu/uscode/text/15/204 http://www.law.cornell.edu/uscode/text/15/204 http://www.nist.gov/pml/wmd/metric/upload/1136a.pdf http://www.nist.gov/pml/wmd/metric/upload/1136a.pdf [2] http://www.ebsinstitute.com/OtherActivities/EBS.qs2df2.html http://www.ebsinstitute.com/OtherActivities/EBS.qs2df2.html http://chronicle.augusta.com/life/life-style/2013-04-04/metric-system-use-rise-us http://chronicle.augusta.com/life/life-style/2013-04-04/metr...