The slow but continuous Rotation of the disc when only the Pressure coils are excited but No current is flowing in the Circuit is called "Creeping". To overcome this creeping effect on no load candition, two holes are drilled in the disc on a diameter, i.e. on opposite sides of the Spindle. This causes sufficient distortion of the field to prevent rotation when one of the holes comes under one of the poles of the shunt magnet.