A temperature calibration is a reliable, reproducible and documented comparison of one piece of equipment under test (data logger, sensor, thermometer) with another piece of equipment that has been temperature calibrated and referenced to a known set of parameters.
check how it reads the temperature of two physical constants: the temperature at which ice melts and the boiling point of water (although the latter should be corrected for atmospheric pressure).compare its readings to a reference thermometer at two known temperature points: 0°C/32°F for ice water and 100°C/212°F for boiling water.