Physical measuring device (also known as a spirit level, hydrometer, or gleucometer) for determining the specific gravity or relative density of liquids. In contrast, a pycnometer is used to determine the density of solids or liquids by weighing, and an aerometer is used for gases. The name areometer is derived from the Greek "araios" (thin) and "métron" (measure, scale), hydrometer from "hýdor" (water).

The measurement of alcohol concentration, which is based on the principle of the plumb bob described by Archimedes (287-212 BC), was already known in ancient times. Archimedes' principle states that a body is immersed in a liquid until the weight of the displaced liquid equals the weight of the immersed body. The most important inventors in connection with viticulture, after whom the units of measurement are also named, were August W. von Babo, Karl Josef Balling, Antoine Baumé, Christian Ferdinand Oechsle and Fritz Plato.
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