 When the power is switched on, the heating element heats the PTC resistor, increasing its resistance to a point where degaussing current is minimal, but not actually zero.In older CRT displays, this low-level current (which produces no significant degaussing field) is sustained along with the action of the heating element as long as the display remains switched on.To repeat a degaussing cycle, the CRT display must be switched off and left off for at least several seconds to reset the degaussing circuit by allowing the PTC resistor to cool to the ambient temperature; switching the display-off and immediately back on will result in a weak degaussing cycle or effectively no degaussing cycle.