Abstract: In a stand-alone or add-on sorter for a reproduction machine, the sorter has access to its own collection of diagnostic programs under control of a single push button carried on the sorter housing. A lamp associated with the push button is used to indicate, as by its frequency of pulsing, the diagnostic state of the machine, and a manually-operable switch is used to move the sorter between its normal and diagnostic modes. When in its stand-alone configuration, the number of successive sorting operations to be carried out by the sorter, before returning to its home position, is controlled by the number of successive operations of the push button, with the switch being in its normal position.