magnetic Indicator

If you hold the indicator in front of an AC field that is strong enough, the red white disk is inside the indicator they begin to rotate in one direction. The rotation of the disc indicates that an AC field exists at this location

the AC display addition, this indicator can be used as a rotation tester for certain circulation pumps. The indicator is held in the center of the motor of the pump and the red white disc is in the same direction as the motor of the pump rotate