Resistors are important parts of circuits that restrict the flow of electricity (see Introduction to Circuits in Figure 1.1) While most resistors have fixed values, thermistors are fancy resistors (see Introduction to Circuits) because they change their resistance based on the temperature of the environment around them. Warm temperatures cause low resistance values, while cold temperatures cause high ones. If we know how resistance varies with temperature, we can use the thermistor to measure resistance, and then convert that resistance to the corresponding temperature. Graphs like the one below are called calibration curves, which enable you to convert a measured quantity (resistance) to its environmental significance (temperature).