Alcoholic proof
Alcoholic proof is a measure of how much ethanol there is in an alcoholic drink. It is commonly used the world over, on the basis that 100 degrees proof is the equivalent of    50 % alcohol by volume (ABV or Alc/Vol). In the United States, it is double the percentage of ABV.  A hydrometer can be used to measure the precise proof of a spirit. This test has gone through many formal changes.