It is an instrument which can detect/calculate very small electric currents. It is also called as moving magnet galvanometer. It has of three circular coils of insulated copper wire wound on a vertical circular frame made of nonmagnetic material as wood or ebonite. A small size magnetic compass needle is pivoted at the centre of the vertical circular frame. These needles go freely in a horizontal plane inside a box made of nonmagnetic substance. When the coil of the tangent galvanometer is include in magnetic meridian and current passes by any of the coil then the needle at the centre gets deflected and comes to an equilibrium position under the action of two perpendicular field: one because of horizontal component of earth and the other because of field set up by the coil because of current (B).