Working of 1 phase dynamometer type power factor meter : The current coil is connected in series with load. Two pressure coils marked as A and B are connected across the supply terminals and take current IA and IB respectively. The current IA is in phase with supply voltage V as its circuit is resistive. While IB lags V by approximately 90 as its circuit is highly inductive. The magnetic field is produced by current coil and two pressure coils, carrying less current. Hence force is exerted on coils A and B. The coil winding are arranged such that the torques on them acts in opposite direction. When both torques on coil A and B, TA and TB respectively, become equal, the moving system becomes stationary and the pointer shows steady deflection corresponding to the power factor of the load.