Oxidation is a process in which a molecule or ion loses electrons. Reduction is a process by which electrons are gained. A measurement of the potential for these processes to occur is called ORP (Oxidation Reduction Potential). Hanna''''s ORP meter is a unique hand-held tester developed to determine this value. The 50-HI98121 is a waterproof ORP, pH and temperature meter. ORP can be measured in a range of +/-1000mV and temperature can be displayed in °C or °F. The meter is factory calibrated and measurements are highly accurate with a unique stability indicator on the LCD. 50-HI98121 provides a battery level indication at startup and the Battery Error Prevention System (BEPS) avoids erroneous readings caused by low voltage level.