A while ago I serviced a JUF/Schatz 400 day clock stamped 12 52 on the back plate, December 1952. I set up the Microset to use the optical sensor and connected it to my laptop. Initial inspection of the escapement seemed ok but later I saw this trace on the laptop. Obviously something very wrong. Closer inspection of the escapement showed occasional mislocking, the pallet flicking back to the impulse face. I was surprised that this produced an easily detected disturbance to the pendulum. After adjusting the position of the fork and regulating the movement the trace looked like this. Job done.