My friend has has been using GM Tubes for more than a decade now. He has been calibrating them once per year. But the calibration data reveals that his GM Tubes would have remained within allowed error range even if he had never calibrated them after the first calibration. Can I use this operaring experience to calibrate my GM Tubes (same manufacturer, same type, same working environment) after a decade?
I know that calibration frequency is:
Recommended by manufacturer.
Adopted by end user based on his own experience, as they might have different operating environment.
What is the correct method of defining calibration frequency without risking safety as well as keeping in view economic considerations?