Photo overview of original Lisp keyboards

I know this is another "neckbeard" comment (love that term), but anyone who ever used the Tom Knight MIT-AI lab keyboards knows in his heart that those were the best keyboards ever made by mankind. Seriously.

They were made by Microswitch (a long defunct subsidiary of Honeywell) and used Hall-effect (mechanical throw) switches with the smoothest throw you've ever felt in your life. So smooth that typing was more like swimming in thought than hitting keys. Sigh, I miss those things every day even after 30 years...

Even the second-generation (first-generation Lisp Machine) keyboard that John Kulp originally had manufactured (all custom-made & designed of course) for the Fusion Lab video terminals (had one in my office when I worked for the MIT-EECS department) were astoundingly good, if not quite as good as the TK keyboards.

What was the thumbs-up key for?