Non-Linear
Thermistors have a non-linear relationship between resistance and temperature, meaning that as the temperature changes, the resistance doesn't change in a straight-line pattern. The behavior of thermistors can be described using the Steinhart-Hart equation or the B equation.
The B equation is simple to calculate using the B value, which you can easily find online. On the other hand, the Steinhart equation uses A, B, and C coefficients. Some manufacturers provide these coefficients, but you'll still need to calibrate and find them yourself since the whole reason for using the Steinhart equation is to get accurate temperature readings.
In the next chapters, we will see in detail how to use B equation and Steinhart-Hart equation to determine the temperature.