If temperature is important in your process, calibration tests are essential to verify that the thermometer you are using is accurate. Electronic Temperature Instruments (UK) manufacture a range of portable dry-well calibrators, fromheat sources to heat/chill sources and fixed temperature checkers that will check the accuracy of your thermometers.
It is recommended that thermometers and temperature monitoring
equipment be calibrated regularly. Thermometers that are in constant
use and used in critical areas should be calibrated more regularly. The
definition of a regular calibration check is very much at the discretion
of the user. For example, a food processing company may well decide
to check their thermometers daily before use, whereas a restaurant
may decide that once a week is adequate.