A thermometer that consistently gives readings that are five degrees cooler than the actual temperature is reliable not valid.
Thermometers are instruments used for measuring temperature of solids, liquids and gases. The thermometer is composed of two important elements; the part that ensures the transformation of physical change into a numerical reading and the temperature sensor. The common types of thermometer include Galileo thermometer, mercury-in-glass thermometer, Infrared thermometer and alcohol thermometer.