Milwaukee OPR Solution 200-275 mV (MA9020) is a lab grade ORP 200-275 mV solution certified to meet the range. Milwaukee OPR Solution 200-275 mV is used to check the health and acuracy of an ORP electrode. Milwaukee solutions are designed to help you achieve reliable and repeatable ORP measurements. Milwaukee OPR Solution 200-275 mV+ fundamental for the correct use of ORP electrodes and for obtaining the most accurate and reproducible readings+ sealed against light with air tight, tamper proof cap+ ideal for fast accuracy check+ simply open bottle, pour small amount into a beaker or container and insert the tester or electrode to start the ORP mV check process