A Manual Water Level Meter typically consist of a pair of insulated wires whose exposed ends are separated by an air gap in an electrode and containing, in the circuit, a source of power. When the electrode contacts the water surface, a current flows through the tape circuit and is indicated by a, light, and audible signal. Tapes are typically marked at 0.01 ft. Some tapes are marked at to 0.05 to 5 ft intervals, particularly tapes that are used in deep wells. The accuracy of electric tapes is considered to be +- 0.02, but may be as great as 0.1 ft.