The API Scale was selected in 1921 by the American Petroleum Institute (API), the U.S. Bureau of Mines, and the National Institute of Standards and Technology (NIST) as the standard hydrometer scale for petroleum products. The API Scale is based on the formula below.
The thermometer scale for VEE GEE® Hydrometers (w/ Thermometers) is located in the body. A correction scale for conversion of readings to 60°F is printed opposite the temperature scale.
