A device, also knows as a scale areometer, hydrometer, or spindle, for determining the density of liquids, is used in printing technology to measure the concentration of alcohol in water-containing process liquids. The device consists of a sealed glass tube filled with air with a weight at one end. Once the areometer is placed in the liquid being tested, it floats either higher or lower, depending on the density of the liquid. The density can then be read off using a scale. This scale is graduated in special units (B? after Baum? or Brix), or in the case of specialist areometers directly in the concentration being measured (alcohol concentration in the case of alcometers, sugar concentration with saccharimeters, etc.). Because the density of liquids changes with temperature, the scale of an areometer is always relative to a specific temperature. To make correct measurements easier to obtain, some areometers also feature a thermometer.