Twin electromagnet coils are provided for increased power [hand driving torque]. The electromagnets briefly pull back against the tension of a spring on receiving a short electrical impulse from the master clock. When the electrical impulse stops the magnets switch off and the spring then pushes the clock hands around by a half minute every 30 seconds.
This method of doing things avoids the movement being made to physically overcome a complete lock-up in the drive to the clock hands. The spring isolates the electro-mechanical drive system from potential damage.
There is a large, brass, spoked wheel visible in the middle of the mechanism. This is not the drive wheel but belongs to the heavy-duty motionwork. As does the partially hidden wheel on its left. Their respective drive pinions are out of sight in the upper image. The drive wheel is almost hidden behind the large wheel but can be recognized by its 120 ratchet-shaped teeth.
A rotating, air-brake "fly" is visible on the far left of the movement. This is presumably to avoid the hands accelerating out of control in the event of serious clock hand imbalance. Turret clock hands are almost always balanced with counterweights. Which adds to the moment of the already heavy hands.
Advancing the clock hands to set the time requires that the direct drive and hand locking provided by the slave are interrupted. At such moments the system is more vulnerable to overrun through imbalance. Possibly through icing, flocks of birds resting on the hands or even from high wind forces. Even if the slave "clock" keeps accurate time it will still be required to be re-set to summer and winter time.
The forked, universal drive joint is seen in the middle of the back of the movement.