The SPER-1E Electret Voltage Reader is specifically designed to make non-contact surface potential (voltage) measurements for all the electret types used in Rad Elec Inc.’s Radon Measurements Products Line. The SPER-1E can be operated from line voltage or batteries. It features a precision, stainless steel shutter mechanism; combined with an electroplated copper electrode for accurate non-contact surface potential measurements. For each electret “reading,” an on-board microprocessor averages 10 sequential voltage measurements and displays the result on the LCD. Comes with carry case, manual, ±ZERO Electret and 2 Reference Electrets.