High end Swiss made movement
There are two barrels, the larger one for the going train and the smaller one for the centre seconds train
Under the cock is a flirt, a lever with a pinion and unequal arms that's driven by the large wheel on the centre seconds arbor, (on the other side of the plate). As it rotates, clockwise, the longer end hits the leaves of the escape wheel pinion but as that's turning in the opposite direction
the lever is released once per second, allowing the seconds hand to jump in whole seconds.
arrow is the stop mechanism for the seconds train, it locks the longer end of the flirt and prevents it hitting the escape pinion, so that the going train continues to run normally, independently of the seconds train.