Both the embossing type and the embossing die are in the station key. This made embossing independent of the number of dies that could be fitted in the clock, and thus allowed use of a large number of differently-numbered stations. The system was invented at Hardinge Bros. of Chicago to get around Newman's patent which required one of the elements to be on the key.

Patrol Recorder
(Recorder shown here is a demonstration unit, with one side cut away)

Hardinge Bros. Patrol