One straight across motion of the pendulum will count as a ‘swing’ (to the other side) – not over AND back – for most pendulum devices that have an ‘over and back’ path. So, for example, an ‘over and back’ pendulum device could attempt one task on the path over, and a second task on the way back.
The exception being…if the pendulum motion results in a noticeable elliptical or circular path (not over and back), then the complete revolution would count as a ‘swing’ for judges. This is largely due to it being difficult for judges to determine anything but one completed revolution for this type of pendulum path.