Our modern pearl grain, troy grain, and avoirdupois and apothecaries' grains all derived from the wheat grain. The carob, or locust tree, produces edible seed pods that are still important as feed for livestock and as a flavoring. Traders used the inedible seeds as a standard weight from which our modern metric carat evolved. Carat weight was standardized in the early twentieth century. If you had purchased a 'one-carat' diamond in 1895, it might have weighed anywhere from 0.95 to 1.07 metric carats, depending on where you bought it.
Consumers sometimes confuse the terms carat and karat.
When you tell people one diamond weighs more than another, they usually understand what you mean-but few consumers realize how precisely diamonds are weighed. In other words, it takes almost 142 carats to equal 1 ounce. But even this is not precise enough for something so precious. The term point can confuse consumers, who may think you are referring to the number of facets on the stone, or to the decimal point specifying hundredths. It will probably be reinstated in future revisions.