These values have not been codified, but have been published in the Federal Register to provide guidance to manufacturers for the nutrients listed (58 FR 2206 at 2213; January 6, 1993). The abbreviation "IU" is used for International Units, "mg" for milligrams, and "mcg" for micrograms. The abbreviation "µg" may also be used for micrograms. Also, the agency has modified the units of measure for four nutrients. Calcium and phosphorus values are expressed in mg and biotin and folate values in mcg (60 FR 67164 to 67174).