DCVG Surveys have been in use for approximately 30 years and are used to locate coating defects or holidays. DCVG surveys are the measurement of the voltage drop between two electrodes placed on the surface of the ground, due to current flow in the soil to a defect or holiday in the pipeline coating. These measurements have traditionally been taken using an amplified analogue voltmeter, with the operator watching the swing of the pointer or needle as the rectifier turns on and off. Modern survey equipment utilizes digital techniques to measure and record the voltage between the two electrodes, recording both the voltage when the rectifier is on and off as well as the GPS coordinates and time of each reading. Some digital  meters use a bar graph in place of an analogue meter to indicate deflection direction and  magnitude.