NIST Publishes Guide to Units

The National Institute of Standards and Technology (NIST, Gaithersburg, Maryland) has published a reference guide to the modern metric system that covers the correct U.S. usage of metric units. "The International System of Units (SI)" describes recent changes in the system since 1998. The publication includes accepted spellings of various units as well as a chapter on units for quantities that describe biological effects and symbols for expressing values for enzyme catalytic activity. The U.S. Omnibus Trade and Competitiveness Act of 1988 designated the metric system as the preferred weights and measures system for U.S. trade and commerce, and U.S. Public Law 110-69 in 2007 replaced the old definition of the metric system with the SI definition.