I don't _know_, but possibly... DEC made a panel with a lot of blinkenlights on it, and nothing more. I've seen one on the DX11 (IBM channel interface for the PDP11), it could also be used with the RK11-C, and quite likely other disk (and tape?) systems of a simialr vintage. In general it displayed the contents of the main control registers of said device and other useful signals. What I can't rememebr is how many lights it had. Something tells me it was eitehr 72 or 144. It was caonencted by a number of paddleboards with 36 pin edge finters, and all pins were used fro signals. It ran off an 8V PSU, and used the 0V of the PSU as the logic references (which therefore had to be linked to the system 0V rail. -tony