Eisco Labs Tangent Galvanometer measures an electric current by determining the magnitude and direction of the horizontal component of Earth's magnetic field. This includes an aluminum 45mm body compass. Features copper magnet wire, adjustable potentiometer, compass and non-magnetic stand. Students can place the compass needle parallel to the coil, pass an unknown current through and measure the angle of deflection. 8" x 5" heavy duty base. D cell battery operates this device, Batteries not included.