Mentioned in literary texts from Late Antiquity, this device was probably already known in earlier times. Used to measure with precision the density of fluids and the specific weight of bodies, it consists of a glass vessel containing a float with sinker, surmounted by a graduated rod. When a weight is attached to the bottom of the float it sinks in different manner depending on the fluid in which it is immersed. Especially useful for detecting the often fraudulent ingredients of wine, it operated according to the principle of Archimedes.