Jewel Unit is a term used to describe the measurement of weight for precious stones, such as diamonds. The unit of measurement is the CARAT, which is equal to 200 milligrams or 0.2 grams. A CARAT is divided into 100 points, so a diamond weighing 0.25 carats would be referred to as a 25-point diamond. The CARAT is the standard unit of measurement for diamonds and other precious stones, and is used to determine the value of the stone.