This seemed to be the video terminal of choice in the early days of computing, for those who owned computers that required an external display or terminal: Altair, IMSAI, most notably. But a million others also.

I have two of these; An ADM-3 and an ADM-3A. The 3A differs most noticeably in that it included cursor controls. Both of my terminals have the lowercase option installed. I have recently cleaned the pots and adjusted the CRT controls in both, and they work just fine, old age not withstanding. 

Lear Siegler must have made ten million of these things, I have seen them everywhere!