oxidation-reduction potential orp is an abbreviation that represents the oxidation potential of the solution. orp value is a measure of the ability of the redox solution, the unit is mv. orp meter test solution redox potential of special equipment. with data lock function to facilitate the measurement and recording of data stored   negative potential (o.r.p) pen       the main technical indicators: measuring range range: 0 ~ ± 1999mg/lmv resolution resolution: 1mv accuracy: accuracy: ± 5mv