ORP standard solutions allow you to test the precision of ORP electrodes. For example, by immersing the electrode in HI7020 solution, you should read within the 200 to 275 mV range (@20°C/68°F). If the reading is outside the indicated interval, clean and condition your ORP electrode in HANNA® pretreatment solution. Use HI7092 for oxidizing or HI7091 for reducing pretreatment.