In establishments where managers take regular inventories, bartenders sometimes add water to liquor bottles to cover up pilferage and free drinks. It's a good idea to spot check your establishment's bottles to keep from being fooled by devious employees. This popular 11" hydrometer gives management the ability to quickly test the alcohol volume in liquor. Reads from 0% - 100% alcohol by volume and also by proof. Alcohol volume is exactly half of the proof. An 80 proof liquor should be 40% alcohol by volume.