Rhode & Schwarz LogICscope?

Went shopping today and found one of these. Is anyone familar with them? I guess it does the same thing as a HP Logic Clip but it's bigger. It has a clip the attaches to a 16 pin IC then about a 18" cable. On the other end of the cable is a box that measures about 4 1/2" x 3" x 1/2" with a large window on one side. Inside the window is a black panel with two rows of holes with a LED under each hole. The odd thing is that one row has eight holes and LEDs and the other has nine! I've been playing with it and haven't seen the 9th LED light up yet so I'm not sure what it's for. There also a slot at the end of the box, It looks like it's intended for the user to make a THIN paper label and insert it under the window and between the rows of LED holes. I opened it up and it's made of individual components (including lots of diodes!) except for three 7404 ICs. The ICs used in this one are all dated 1972. The whole thing is grey except for the window and it says that it was made in West Germany. Anybody know exactly what the extra LED is for? Joe