Typically you would start at a higher frequency and reduce after enough conclusive evidence that the equipment is not going out of calibration.

Unfortunately that means it is going to be different for everyone and everything. The metal detectors are checked at start up, hourly & product changeover and at the end of the run with 3mm ferrous, 3mm non ferrous and 4mm stainless steel test pieces.Д¬alibration should be determined by the history of the tools/machines being calibrated along with the potential for failure and the risks associated with the failure. The scales are checked weekly and the weighheads 3 monthly as these are not a food safety risk of they are not functioning. The staff will be using the equipment and would not be able to tell if the probes are working & reading properly, other than on or off. I have found it easier and cheaper to buy a new master probe with calibration certificate each year (just before BRC audit) than to send off to get an old one calibrated. The records showed that the risk of the probe being found to be out at the weekly check was low. This is done monthly after 5 years of weekly checks. In my risk assessment I put it that the thermometers would be either working or not working as a guideline rather than a sliding scale of say being more than 2 degrees centrigrade out. We annually calibrate metal detectors, scales, weighheads (we are a bakery) and are verified weekly and monthly. There is a difference between external calibration and internal verification.

Calibration schedule template