The temperature coefficient of resistance, known as alpha and measured in percent per degree Celsius, is the ratio at a specified temperature, T, of the rate of change of zero-power resistance with temperature to the zero-power resistance of the thermistor. The material constant of an NTC Thermistor, known as beta and measured in degrees Kelvin, is a measure of its resistance at one temperature compared to its resistance at a different temperature. The reference temperatures used in the formulas here for Ametherm’s thermistors are 298.15°K and 348.15°K.