The Callendar-van-Dusen-coefficients are used to describe a polynomial function of the actual characteristic of a platinum measuring resistor. This can be stored in a transmitter and thus increases the accuracy of the entire measuring chain. To calculate the Callendar-van-Dusen-equation in the temperature range over 0 °C, the resistance at 0 °C and two other test temperatures are collected by comparative measurements. Hence, the a and b constants are calculated. For the negative temperature range, the inclusion of a measured value for another test temperature is needed in order to determine the d constant. One can, however, represent the characteristic curve of the platinum measuring resistor just as well mathematically using the polynomial equation per DIN EN 60751 with the constants A, B and C (see also WIKA data sheet IN 00.17, page 4) and also determine these by calculation from the measurement of 3 (or 4 at t < 0 ° C) test temperatures. Similarly, one can convert the constants A, B, C into the Callendar - van Dusen constants.