A trimmer potentiometer is a miniature adjustable electrical component. They're designed for "set and forget" applications to "trim" the value of a resistor in order to provide an exact gain, output voltage, or current. They are common in precision circuitry like A/V components, calibrating instruments and setting the bias current on power amplifiers. Trimmer potentiometers are mounted directly on circuit boards, set with a small screwdriver and designed for few adjustments during operation. They may either be single or multi-turn, with the multi-turn used in applications that require more precise settings. They can also be mounted either vertically or horizontally, depending on the requirements for adjusting the component. In 1952, Marlan Bourns patented the first trimming potentiometer, calling it the "Trimpot".