The pH meter has two calibration points. Thecalibration can be done with the trimmer on the side of the device which isprotected under a cover. With this combined device, the user can determine pHvalue, temperature or Redox potency (ORP). For the latter measurementparameter, a Redox electrode must be ordered separately from the PCE-228 pHmeter. We recommend the ORP-14 electrode. The pH meter is powered by a 9Vbattery which is included.