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| | Measurements, Units of Measurement, Weights and Measures - Numericana |
 | | A mole of "objects" [atoms, molecules, ions, electrons] is defined to be as many of these as there are atoms in 12 grams of carbon-12. |
 | | The labeling of A/C units is in terms of thousands of Btu [per hour] (typically: 024, 030, 036, 042, 048, or 060), but betrays its origin in terms of tons of cooling (2, 2½, 3, 3½, 4, or 5 tons of refrigeration). |
 | | The US gallon, the so-called Winchester gallon, is now defined as exactly equal to 231 cubic inches (this odd value comes from rounding up the volume of a cylindrical measure 7 inches in diameter and 6 inches in height, which dates back to the days of the Magna Carta). |
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