Two-component model that simulates a burst with a fluctuating EVPA. Panel a: the burst EVPA has an overall slope of −3° and is modulated by a sine function with amplitude 6°. Panel b: the sum vector makes three loops on the (Q, U) plane, with the middle loop enclosing the origin. The jet, burst and sum vectors are shown at t = −6. The arrow shows the direction of time. Panel c: the EVPA shows a non-monotonic CW swing of 180° plus a small overshoot. Note that the Q and U scales in (b) are different.