Overhead demonstration thermometer is a 10" dual-scale transparent model with an adjustable red bar to indicate temperatures. the left side shows the fahrenheit scale from -40° to 212°; the right side shows the celsius scale from -40° to 100°. each scale has marks labeled for every ten degrees, with smaller subdivision marks between them to indicate temperatures to the nearest two degrees. although there are several types of thermometers, this overhead thermometer represents the liquid-in-glass type, which is the best known. the liquid- in-glass thermometers are used to determine the temperature in or outside a building, to measure body temperature, and for cooking. the adjustable red bar on the overhead thermometer represents the liquid contained in real thermometers. here’s how it works: the liquid fills a glass bulb connected to a sealed glass tube partially filled with liquid. when the temperature goes up, the volume of the liquid expands and the liquid rises. a temperature scale is on the outside of the thermometer, alongside the glass tube, to indicate the degrees fahrenheit or degrees celsius.