Corrosion of steel is an electrochemical process involving anodic (corroding) and cathodic (passive) areas of the metal. By measuring concrete - surface electrical potentials relative to a standard reference electrode on a predetermined grid, the presence and location of corrosion and its probable future performance may be assessed. It is possible, by regular measurements, to monitor the behaviour of new and relatively new structures and thus minimize maintenance costs. Measurements automatically converted and displayed as copper/copper sulphate equivalent potentials.