The Extech RE300 ExStik ORP Meter with Flat Surface ORP Electrode measures ORP/Redox from -999 to 999mV in high resolution of 1mV. It features automatic electronic self-calibration, Data validation indicators, Data Hold, Auto shut-off and low battery indication. Additionally, the RE300 has a simulated analog bar graph that displays change in ORP reading and its memory stores and recalls 15 readings and saves last calibrated value.