A hydrometer is an instrument used for measuring the relative density of liquids based on the concept of buoyancy.... The liquid to test is poured into a tall container, often a graduated cylinder, and the hydrometer is gently lowered into the liquid until it floats freely. Provides measurements of alcohol content in proof of spirit and tralles (percent of alcohol by volume). Used only for distilled spirits, not fermented beverages like beer, wine, mead and cider. Features: proof of spirit scale, 0 to 100. Percent of alcohol by volume scale (Tralles) 0 to 100. Specs: For distilled spirits only. Will NOT work for fermented beverages like beer, wine, cider and mead. Made of glass. 11 3/4" L. Includes: Protective plastic storage case.