Abstract: Apparatus for monitoring the concentration of toner particles in an electrographic developer mixture having toner and carrier particles in which a first signal is produced representative of the reflectivity of the developer mixture and an offset signal is produced representative of changes in the reflectivity of the developer mixture caused by the build up of a film of toner on the carrier particles. A computation device such as a digital computer in response to the first signal and the offset signal provides a correct representation of the concentration of toner in the developer mixture. When the toner concentration is below a desired level, the computation device actuates a toner replenishment mechanism which adds fresh toner to the developer mixture.

Abstract: Copy finisher for assembling uncollated or collated copies produced by an electrographic copies into booklets in an intermediate tray, for stapling the booklets, if desired, and for selectively stacking the booklets in an offset or straight manner in an output tray. If a malfunction, such as a paper jam, occurs in the copier, the finisher will assemble the copies in process in the finisher into a booklet and offset stack the booklet in the output tray. If the number of copies in a copy set produced by the copier exceeds the copy assmebling limit of the intermediate tray, the finishing apparatus will assemble the copies of the set into subbooklets of copies equal to or less than the copy limit of the intermediate tray and stack all of the subbooklets of a copy set at the same location in the output tray.