Precision thermometers, based on the principle of resistance thermometry bridges such as the Wheatstone bridge, ensure accurate temperature measurements at the resistance thermometer (RTD). The calibration is crucial and, for this, the resistance value of the RTDs is measured at different known temperatures with a precise calibrator. The bridge circuit, usually a voltage divider, enables the adjustment conditions to ensure accurate measurements. The internal resistance of the RTDs must be taken into account in order to precisely react to the conductivity and impedance. The calibration involves both voltage measurement and current measurement, using a defined measuring current level. The measuring results are displayed on a voltmeter or a moving-coil movement and the reading represents the measured value of the RTD. Calibration is carried out periodically to ensure long-term accuracy and traceability to international standards is essential. All these steps ensure reliable temperature measurements in various applications.