By the end of the 17th century England had introduced tests based on specific gravity for defining proof. However, it was not until 1816 that a legal standard based on specific density was defined in England. 100 proof was defined as a spirit with the specific gravity of pure water at the same temperature. From the 19th century until 1 January 1980, the UK officially measured alcohol content by proof spirit, defined as spirit with a gravity of that of water, or 923 kg/m3, and equivalent to 57.15% ABV.