High-precision temperature measuring technique presupposes a high standard of quality of all components of the measuring system. Most important is the temperature sensor. Thermistors have been proved good for long-term stability in a limited temperature range from – 20 to + 50 °C. The non-linear characteristic of the thermistor can be mathematically described. Multislope analogue-digital converters with very high resolution applying compensation measuring methods are efficient for the exact determination of absolute temperatures with an accuracy better than 1 mK resolution.