The Half Cell Potential (HCP) method is used when monitoring the corrosion activity, resistivity, and rate of reinforcing and other structural steel elements embedded in concrete. This is an electrochemical technique used to locate areas of active corrosion of steel reinforcement in a concrete slab or wall. The HCP method takes advantage of the oxidation-reduction (redox) chemical reaction from active corrosion that produces an electrical potential that can be measured externally. A refinement of the basic HCP method is the Galvanostatic Pulse Measurement (GPM) method. This method is used by the GalvaPulse™ and CorroMap™ instruments from FORCE Technology. The GPM method allows not only the determination of the location of active corrosion, but also the estimation of corrosion rates in terms of diameter loss versus time.