The US system comprises three systems of weight and mass: avoirdupois (the common system), troy (used mainly by jewelers), and apothecaries’ measure. Although confusion is unlikely, an abbreviation can, if necessary, be referred to the appropriate system thus: lb. av., lb. t., lb. ap. Also, the systems of capacity measure used in the United States and the British Commonwealth differ (an American pint being more than three ounces smaller than a British pint, for example), but the same abbreviations are used.
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Weight or mass |
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Dry measure |
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Liquid measure |
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As with length and so forth, abbreviations do not change in the plural.