Tangent Galvanometer -A bakelite ring or bobbin is of 165 mm diameter with 3 windings of 2, 50, & 500 turns. The magnetometer is supported on a brass tube fitted on an ebonite plate which is free to revolve in the base of the instrument. The magnetometer & the ring can both be rotated independently of the base which is with levelling screws. The compass box consists of a bakelite base with metal dial of diameter 100 mm graduated in degrees & with anti parallax mirror. Cobalt steel magnet & aluminium pointer are mounted on special synthetic sapphire. The needle moves on special pivot. This combination makes the needle virtually frictionless.