Carats?

The word "carat" originated from a natural unit of weight: The seeds of a carob tree.

Diamonds were traditionally weighted against these seeds until the system was standardized and one carat was fixed at one-fifth of a gram.

A carat is divided into 100 "points," so that a diamond of 50 points weighs half of a carat.

Remember that because "carats" are based upon weight, not all 1-carat diamonds will appear to be the same size.