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A galvanometer detects electric current through a mechanical response, such as the deflection of a pointer.^[ref]

A sensitive galvanometer makes a small electric current visible; a calibrated deflection also estimates its magnitude. A center-zero scale distinguishes both signs of electric current. The moving-coil galvanometer rotates a coil in an imposed magnetic field, whereas a moving-magnet galvanometer rotates a magnetic needle in the coil's magnetic field. The spring-balanced model below describes the moving-coil galvanometer, not every instrument called a galvanometer.

A moving-magnet galvanometer measures electric current through the torque it exerts on a movable magnetic dipole moment. A fixed coil carries the current and creates a magnetic field; a suspended magnet turns against a restoring torque supplied by its suspension or a reference field.

For sufficiently small deflections in a calibrated geometry, the coil field and resulting angular response are proportional to electric current. A pointer or reflected optical spot reads the angle. This differs from a moving-coil galvanometer, where the current-carrying coil itself moves. Mechanical damping determines whether the indication oscillates or settles smoothly after a current change.