A RFI canceller, for use in a subscriber line system using multi-carrier modulation, measures a RFI disturbance in carriers falling within a band of frequencies causing the RFI. The iterations create corresponding rankings of the input variables. Both of these processes are performed on the memory in a manner that is externally transparent and, consequently, need not be managed externally by the host or controller to which the memory is attached. If the printer can use these characteristics and they differ from the characteristics that are presently being used by the printer, the printer updates its printing characteristics using the printer data memory’s printing characteristics. The top end of the block is fitted with an air vent tube.