mg is milligauss ? does this will help zeroing the device inside a radiation tissu please? In fact i lack the knowledge to undestand this setting . i think zero-mf was more simple since you just hit the button then it setup the thing in a zero radiation environnement.
To set the EMF 390 to zero inside anti-radiation material, you'll need to calibrate the device. Check the settings menu for calibration or baseline options, then follow the instructions in the manual. If there isn't a specific "EMF zero" setting, look for similar options to reset the readings.