The Tektronix DF2 is a display formatter for use with the 7D01 logic analyzer. It is a DF1 with special support for debugging GPIB (the DF2 does not, however, have a GPIB interface of it's own - it can only analyze it). An GPIB <-> probe comb adapter was supplied with the DF2. This functionality is invoked with the added MENU control. Refer to the instruction manual for details.