Clocks of this model were imported from Germany without the registration mechanisms, which were produced by Corbin Cabinet Lock Company and fitted to the clocks in the Eco plant in Boston. The principal of the marking mechanism is that of a cylinder lock. The station keys, which had the characteristics of a Yale-type cylinder key, would only turn in clocks "keyed" to match.  When a proper key is turned, a lug on the end of the key depresses the tumbler that corresponds to that particular station and thereby pricks the dial in the annular ring reserved for registrations from that station.

Yale-type Marking Mechanism

Array of Marking Tumblers
Station Key