How often for calibrate?---Jerry say: if you want to have an accurate measurement, before start to calibrate, please warm machine 15 minutes in every day. Evey 4 hours re-start cailbrate. but for normally user:after cailbrate once time, please measure one sample cable, and then every day, you can take the same sample cable to test before you measure, if the valus is the same (or be close to), you cann't need to cailbrate.