Once more, we are talking of the device described in fig 20.
In the text it says that the way to make a single blow is to go quickly from holding up mode (fig17) to working mode (fig 16) and back again, and to do this within a working cycle.
The device -as I understand it- helps you to press the lever at the right time, so to speak. And when the right time is, is censored by the adjustable screw no21 ( fig 20) who reads the position of the pumping piston. Since it is as you say Frosty “a strictly master-slave system” I would argue that in a way a sensor is reading where the tup is, even if its isn't read from the tup itself.
On my Anyang I think it would be easier to read the timing on the flywheel since the pumping piston isn't easily available.
What I was interested in was if any one had used the arrangement and if it was well working. Without having used it I feel that there might be reason to also include a way to stop after a full cycle, but maybe that isn't necessary.
Robin