An electronic postage meter includes electronic circuitry for providing an accounting of the number of mailpieces imprinted with postage, and the amount of postage imprinted on such mailpieces. An electro-optic sensor connects with a mechanical drive of a printing drum of the meter to sense successive...http://www.google.de/patents/US4573174?utm_source=gb-gplus-sharePatent US4573174 - Electronic postage meter having interlock between mechanical and electrical registers
