The choice of units of measurement is also laden with history. As settlers began to colonize America, they brought with them measurements from their former countries. These included the English ell for cloth but also the far shorter Dutch ell, the Rhineland rod and the British chain and the Spanish vara for measuring land, the English flitch of bacon and hattock of grain, plus the German quentchen for gold.
By the time of Independence, 100,000 units of measurement were in use, Andro Linklater, a British historian, recounted in “Measuring America: How the United States Was Shaped By the Greatest Land Sale in History.” Opportunities for cheating were rife. Establishing common measurements, and therefore fair trade, became a political imperative.
The first message to Congress by President George Washington, in January 1790, contained a call to lawmakers about the importance of establishing a standard system of weights and measurements. Their solution was to adopt parts of the British imperial system, including the yard. In 1815, a brass yard bar made by the Edward Troughton, a London instrument maker, arrived in the U.S. to become the American standard yard.
By 1850, most states then in the union had received official copies of that yard and the other standards, a bid to make sure that every citizen and enterprise in the nation had equal access to the same units of measurement.
But imperial measurements, while standard, were also arbitrarily derived. The yard, for instance, evolved from the idea that “foure graines of barley make a finger, foure fingers a hande, foure handes a foote,” Mr. Linklater noted. During the reign of Elizabeth I, those 16 fingers per foot became 12 inches and were tripled to make the yard that Mr. Troughton fashioned into a bar for America.
Even as the U.S. government shipped imperial standards across the country, the move to metric was gaining appeal in America and elsewhere, driven by a hunger for ever greater precision and easier replicability. Decimalized metric standards, which were being developed by French scientists at the urging of its National Assembly during the French Revolution, are based on scientific findings rather than folksy norms, and these days units increasingly relate to each other. The meter was originally based on one ten-millionth the distance from the geographic North Pole to the Equator; it is now derived from the speed of light. Volume and mass, in turn, are based on the meter.
By 1866, Congress legalized the use of metric units across the U.S., setting the meter 39.37 inches long, and in 1875, America was among the original 16 signatories of the Treaty of the Metre, which aimed to establish metric standards across the world. America broke with the imperial system of measurement in 1893 and officially adopted metric standards under the order of Thomas Mendenhall, then the superintendent of the U.S. Coast and Geodetic Survey, the forerunner of the National Geodetic Survey.