As the flux in the ring is increased from 0 to the magnitude of increases to a maximum. As the flux is increased greater than it is now energetically favourable for a current, , to flow in a clockwise direction, decreasing in magnitude to 0 as the flux reaches . The circulating current has a periodic dependence on the magnitude of the applied field, with a period of variation of , a very small amount of magnetic flux. Detecting this circulating current enables the use of a SQUID as a magnetometer.