Measuring with an NTC

It is often desirable to know how hot a part is. The usual method is to use a thermometer to measure the temperature, but this may not always be practicable.However, with the help of a small NTC and a multimeter it is just as easy. During the development of a speed controller with a final stage consisting of MOSFETs, it was necessary to measure the temperature of these devices. A normal thermometer is unsuitable for this purpose, so a search was made for a sensor that could be secured to a MOSFET.We found an NTC resistor, type 46720055, in the Conrad Electronics catalogue that appeared eminently suitable. The NTC has a flange with a hole with which it can be secured using a screw. This was exactly what we needed. But how could the measured resistance be easily converted to temperature?