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a unit of weight, abbreviated kar. in Russian and ct internationally, which is used in the jewelry trade for measuring the weight of precious stones and pearls. The carat is used in a number of countries to indicate the purity of precious metal alloys. The metric carat, which was established by the fourth General Conference on Weights and Measures (Paris, 1907) and adopted in the USSR in 1922, is equivalent to 200 mg (exactly) or 2 X 104 kg.