Potentiometers & Presets
A potentiometer is a three terminal variable resistor with two fixed terminals and one variable terminal. It is a passive electronic component. It is used as a voltage divider or variable resistor in a circuit. Potentiometers are labeled with prefixes A, B or C. Prefixes refer to the taper, A - audio/log, B - linear, C - inverse audio/log. Audio taper resistance slowly increases between wiper and ground as the knob is turned clockwise until the knee where-after it hits max resistance in hurry, linear, steady flat increase in resistance throughout the travel, inverse audio self explanatory.
A preset also referred to as a trimpot is used to carefully set reference voltage, current or resistance in an electronic circuit. Once set, it is usually not disturbed. Presets are available in different form factors. These are also available as single turn and multiturn devices.