We Americans are known for our strong sense of national pride toward our unreasonable stubbornness against adopting the metric system. We haven't always been so intractable toward what has become the international standard for measuring distance, mass, temperature and other things we need to describe to one another from time to time. We came very close to officially adopting the metric system, just after France did in 1800.
Thomas Jefferson was president at the time and he was keenly interested in units of measurement, having created his own, including the furling (1,000 feet) and the mile (which he reckoned to measure 10,000 feet rather than the customary 5,280 feet). Congress never followed through on adopting the system or any system for the next couple hundred years.
It wasn't until President Gerald Ford signed the Metric Conversion Act on December 23, 1975, that the U.S. ever actually adopted a system of measurement of any kind. Endorsed, yes, encouraged, even, signed up for treaties with other nations, sure. But it wasn't until 1975 that we designated any measurement system as official.
The 1975 Act didn't last very long. You can imagine that American scientists, who had long been using metric units to describe their work to others in the international scientific community, were excited about the conversion. A Metric Board was created by the law to oversee the switch, complete with PSAs and jingles about metric measurements. But your parents and mine decided they weren't in the mood to learn anything new that decade, and public opposition the process of officially converting to the metric system (called metrication). The result was a law passed under Reagan that repealed the metrication in 1982.
But this was not the end of the metric system in America. You can see evidence of the metric system everywhere: soda is sold in two-liter bottles, and booze comes in sizes denoted by milliliters. Your car's speedometer shows your speed in both miles and kilometers per hour. Dry goods like rice are described on the packages their sold in by the traditional and metric weights. A quick glance around reveals an American society surrounded by two systems of measurement.
Surprisingly, this dichotomy is older than it seems. The traditional system of the foot and ounce was first created in 1832 by the Treasury Department for use by customs officials. The U.S. signed the Treaty of the Meter in 1875, and is a member country of of the International Bureau of Weights and Measures, which relies on the metric system. And then there is the Mendenhall Order, named after a Treasury superintendent who, in 1893, decreed that the metric system would be used to describe our traditional units. Hence, a pound is officially equal to 453.59237 grams.
And here we reach the heart of the matter, at least as far as author Andro Linklater argues. The metric system is precise, indeed. It was originally used to describe the distance equal to 1/10,000,000th the distance between the equator and the North Pole, as measured along the Paris meridian. The original surveyors who calculated were off only by 0.023%, by the way. Today, thanks to our deepened understanding of the decay of isotopes, we now know that the actual distance of a meter is 1,650,763.73 wavelengths long of Krypton 86 radiation.
What Linklater supposes, and what is probably as good as any explanation of the baffling mystery of America's aversion to the metric system, is that metric units are precise, while the old-world, traditional units we cling to are human-based. As it's put by one reviewer of Linklater's 2002 book, "Measuring America: how an untamed wilderness shaped the United States and fulfilled the promise of democracy":
"We've seen above that the acre, like most ancient measures, was based on an utterly human scale--in this case the 'area of agricultural land that could be worked by one person in a day.' Metric measures exchange humanity for regularity and precision, sacrifice soul for science."