16 CFR 23.17 - Misrepresentation of weight and “total weight.”
(a) It is unfair or deceptive to misrepresent the weight of a diamond.
(b) It is unfair or deceptive to use the word “point” or any abbreviation in any representation, advertising, marking, or labeling to describe the weight of a diamond, unless the weight is also stated as decimal parts of a carat (e.g., 25 points or .25 carat).
A carat is a standard unit of weight for a diamond and is equivalent to 200 milligrams ( 1/5 gram). A point is one one hundredth ( 1/100) of a carat.
(c) If diamond weight is stated as decimal parts of a carat (e.g., .47 carat), the stated figure should be accurate to the last decimal place. If diamond weight is stated to only one decimal place (e.g., .5 carat), the stated figure should be accurate to the second decimal place (e.g., “.5 carat” could represent a diamond weight between .495-.504).
(d) If diamond weight is stated as fractional parts of a carat, a conspicuous disclosure of the fact that the diamond weight is not exact should be made in close proximity to the fractional representation and a disclosure of a reasonable range of weight for each fraction (or the weight tolerance being used) should also be made.
When fractional representations of diamond weight are made, as described in paragraph d of this section, in catalogs or other printed materials, the disclosure of the fact that the actual diamond weight is within a specified range should be made conspicuously on every page where a fractional representation is made. Such disclosure may refer to a chart or other detailed explanation of the actual ranges used. For example, “Diamond weights are not exact; see chart on p.X for ranges.”