As it is a non-linear device the B constant in a thermistor is needed to identify it. This is the relationship in resistance in a thermistor between two specified points, normally 0-50C, 25/50C, 25/85C and is specified in Kelvin (K) which is calculated using the formula below (Fig 3.)
Fig 3. b = Ln(Rt1/ Rt2) / (1/T1 – 1/T2)
This means in a 10,000 Ω (R25) thermistor, the B value can be 3435K. However, another manufacturers 10,000 Ω thermistor can have a B value of 2976K.
Therefore thermistors can have the same reference resistance of 10,000 Ω at 25 Deg C (R25) but can have different B values, so both values are needed to identify a thermistor.
Another way to calculate the Thermistor RT Curve is to use the Steinhart-Hart method.