 Logarithmic taper potentiometers are often used for volume or signal level in audio systems, as human perception of audio volume is logarithmic.The most common way to vary the resistance in a circuit is to use a rheostat.The word "rheostat" was coined about 1845 by Sir Charles Wheatstone, from the Greek "rheos" meaning "stream", and - -"states" (from "histanai", " to set, to cause to stand") meaning "setter, regulating device", which is a two-terminal variable resistor.