ExStik Waterproof ORP Meter The Extech RE300 ORP Meter measures ORP/Redox from -999 to 999mV. It has an automatic, electronic self-calibration and a simulated analog bargraph that displays fast changes in ORP readings. Additional Features The RE300 ORP Meter has a high resolution of 1mV and a memory that stores and recalls up to 15 readings and it saves the last calibrated value. The data validation indicators show the user that the reading is stabilized and it features data hold, auto shut-off, and low battery indication. This meter has a IP57 waterproof rating. Includes This product comes complete with an RE305 flat surface ORP electrode, protective sensor cap, sample cup with cap, four 3V CR2032 button batteries, and a 48-inch neck strap. In addition, the RE300 can be used with PH105/PH115 electrodes to make pH measurements or the CL205 electrode for making Total Chlorine measurements.