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The only troy weight in widespread use is the British Imperial troy ounce and its American counterpart. Both are based on a grain of 0.06479891 gram (exact, by definition), with 480 grains to a troy ounce (compared with 437 + 1 ⁄ 2 grains for an ounce avoirdupois).
The grain was the legal foundation of traditional English weight systems, [5] and is the only unit that is equal throughout the troy, avoirdupois, and apothecaries' systems of mass. [6]: C-6 The unit was based on the weight of a single grain of barley which was equal to about + 4 ⁄ 3 the weight of a single grain of wheat.
Another difference arose when Britain abolished the troy pound (373.241 7216 g) on 1 January 1879, leaving only the troy ounce (31.103 4768 g) and its decimal subdivisions, whereas the troy pound (of 12 troy ounces) and pennyweight are still legal in the United States, although they are no longer widely used.
(A kilogram bullion bar contains 32.151 troy ounces.) For historical measurement of gold, a fine ounce is a troy ounce of pure gold content in a gold bar, computed as fineness multiplied by gross weight [5] a standard ounce is a troy ounce of 22 carat gold, 91.66% pure (an 11 to 1 proportion of gold to alloy material)
Troy weight, avoirdupois weight, and apothecaries' weight are all built from the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds), the relationship between the grain and these other units within each system varies.
Exceptionally, as can mean the Roman weight or coin. The so-called Holland troy weight (“Hollandsch Trooisch Gewicht”) used a pound of 2 troy marks or 16 troy ounces, instead of the 12 ounces usual elsewhere. Amsterdam weigh-house weight {“Amsterdamsch Waag-gewicht”) was 40 ´´azen´´ heavier to the pound than Holland troy weight.
The 56-pound weight was used as a reference standard as late as 1588. [12] [20] A statute of Henry VIII (24 Hen 8 c. 3) made avoirdupois weights mandatory. In 1588 Queen Elizabeth increased the weight of the avoirdupois pound to 7000 grains and added the troy grain to the avoirdupois weight
Irish gold pistole, bearing its weight (4 dwt 7 gr) (National Museum of Ireland – Decorative Arts and History). A pennyweight (dwt) is a unit of mass equal to 24 grains, 1 ⁄ 20 of a troy ounce, 1 ⁄ 240 of a troy pound, approximately 0.054857 avoirdupois ounce [1] and exactly 1.55517384 grams. [2]