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A pennyweight (abbreviated dwt) is a unit of mass that is equal to 24 grains, of a troy ounce, of a troy pound, approximately 0.054857 avoirdupois ounce 〔Calculated using the relationships: :1 avoirdupois ounce = 437.5 grains :1 troy ounce = 480 grains〕 and exactly 1.55517384 grams.〔Calculated using the relationship: :1 troy grain = 0.06479891 gram (exact by definition)〕 ==History== In the Middle Ages, a British penny's weight was literally, as well as monetarily, of an ounce and of a pound of sterling silver. At that time, the pound in use was the Tower pound (5,400 troy grains). The medieval English pennyweight was thus equal to 32 Tower grains (also known as wheat grains). When Troy weights replaced Tower weights in 1527, the Troy weights were defined in such a way that the old Tower pound came out to exactly 5400 Troy grains (also known as barleycorns), the Tower pennyweight 22 Troy grains (and thus approximately 1.46 grams). After 1527, the English pennyweight was the Troy pennyweight. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pennyweight」の詳細全文を読む スポンサード リンク
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