Despite Americas long history with SI units, measuring remains a mess in the States. A football field traffics in yards while most footraces prefer meters. Mechanics measure the power of an automobile engine in horsepower (foot-pounds per second), but express the same engines displacement in liters. Air pressure is denoted in all sorts of ways: pounds per square inch (or psi) for tire pressure, inches of mercury for surface atmospheric pressure and millibars for air pressure aloft. And these are just a few examples. In the U.S. Customary System, or the inch-pound system, more than 300 different units exist to measure various physical quantities. Many of those units use the same name but have very different meanings. On the U.S. Metric Association Web site, contributor Dennis Brownridge identifies at least nine different meanings for the unit we know as a ton: short ton, displacement ton, refrigeration ton, nuclear ton, freight ton, register ton, metric ton, assay ton and ton of coal equivalent...
Posted on: Sun, 04 Jan 2015 23:21:56 +0000
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