Extech RE300 ExStik ORP MeterExtech RE300 ExStik ORP Waterproof Meter ExStik ORP Waterproof Meter Flat surface electrodes provides On the Spot measurements With 4mV accuracy and high 1mV resolution Key Features: Measures ORP from 999 to 999mV Automatic electronic self calibration Simulated analog bar graph displays change in ORP reading Memory stores and recalls 15 readings and saves last calibrated value Data validation indicators show user the reading is stabilized Large 3 1 2