U.S. Metric Association (USMA), Inc. The U.S. Metric Association (USMA), Inc., with headquarters in Northridge CA, is a national non-profit organization, founded in 1916. It advocates U.S. conversion to the International System of Units which is known by the abbreviation SI (ess-eye). SI is also called the modern metric system. The process of changing our system of measurement units to the ...