Thermistors are one of the most accurate types of temperature sensors. They are resistors whose resistance varies greatly with temperature. This resistor type is used commonly as an inrush current limiter, temperature sensor, self-resetting overcurrent protector, and self-regulating heating element. The two types of Thermistors are based on the sign of k, which represents the first-order temperature coefficient of resistance. If the k is positive, resistance increases with temperature increase and the device is referred to as a positive temperature coefficient (PTC) Thermistor, or posistor. If k is negative, resistance decreases with increasing temperature, and the device is called a negative temperature coefficient (NTC) Thermistor. Both PTC and NTC Thermistors are used in a wide range of applications, including measuring coolant and oil temperatures in automobiles (NTC thermistors), digital thermostats, battery packs, and televisions.