With our soil Redox probes the potential difference is measured between an inert measuring electrode and an integrated or external reference electrode (REF-12-0-A). The potential difference arises from the electron exchange between the redox pairs in the sample (soil, sediment, solution, etc.) and the inert measuring electrode, which is made of platinum in the SWAP soil Redox probes. It does not react chemically, but conducts electrons. The reference electrode provides a constant potential. The SWAP instruments reference electrodes contain 4.76 KCl saturated KCl as standard or 3 M KCl gel for previous versions.

In the (scientific) literature, ORP values are often expressed as mV measured against a standard hydrogen electrode, called SHE. ORP values measured with an ORP probe with a Ag|AgCl -M KCl reference electrode can be converted to SHE values. Several reference electrode potential convertors – to convert potentials between reference electrodes – can be found on the internet (e.g., Reference Electrode Conversion Calculator | Pine Research Instrumentation (see photo).