Do ORP meters need to be calibrated?

No, ORP or Oxidation Reduction Potential meters also called, “Redox”, meters do not need to be calibrated. Some ORP meters have an Offset Adjustment. This adjustment is used when comparing a combination of a particular ORP meter and a particular ORP electrode to a known ORP standard solution. The user can then offset any actual reading by a few millivolts, mV, so the displayed reading matches the value of the known standard. When this is done it is merely a check of the ORP electrode to ensure it is within acceptable limits. Each manufacturer’s quality control limits vary but generally most ORP electrodes, in good condition, perform within about +/- 20 mV of any ORP standard.