Just out of curiosity why is the calibration interval 1yr for lab instruments like DMM, scope etc. Why not 2 years. Also, you use a higher accuracy bench DMM to calibrate a hand held DMM. Instead of getting calibration done by an outside agency, Why not calibrate the handheld DMM yourself using an already calibrated bench DMM. I am trying to ask if "self-calibration" is accepted in the industry.