India Rati
In India, originally the source of most of the precious stones, a weight known as the rati was used. This corresponded to the weight of the black seed of the abrus precatorius, which was something between the present half a carat and seven-eighths of a carat. The weight varied very considerably in different districts and at different times; for example, in the year 1827, one rati was equivalent to 2.114 grains Troy, while in 1896 it equaled only 1.88 grains Troy. In the Golconda district, once a rich source of the finest and largest diamonds, the mangelin was used as the unit of weight. According to Tavernier, this was equal to 1.375 carats. Now, the metric carat is used throughout India, as it is in nearly all countries where important dealings in precious stones take place.
For many centuries, a carat of no very definite weight was in general use; it was not the metric carat, and it had no definite relation to any constant weight or measure. As the years passed, the number and value of stones which came on the market increased. Their use in jewelry became more general, and attempts were made to fix some recognized universal standard of weight by which values could be determined. In the year 1871, it was suggested at a representative meeting of jewelers that a carat should equal .205 of a metric gram, the gram being a convenient weight. The gram represented the exact weight of one cubic centimeter of distilled water at a temperature of 40 Centigrade, and it was a unit already in use in many branches of science.