An electromechanical device used to detect and show an electric current is a galvanometer. A galvanometer acts as an actuator in response to electrical current flowing through a coil in a continuous magnetic field by generating a rotary deflection of a pointer.
This approach offers some inaccuracy since the ideal ammeter must have zero resistance and an infinite resistance voltmeter. But there are no devices. Therefore, to calculate the unknown resistance value, we tend to use the half deflection method. The low resistance parallel to the galvanometer is r.