Well, if anyone has any idea what the word/text on the button in the shadow right under the crewman's hand is, I'd like to know.
Yes, it's "THANTUX," which means nothing as far as I know. For years I've tried really hard to hallucinate that what it says is "THANTUN." (Mr. THANT was the Secretary General of the United Nations (UN) back when Star Trek was on the air, so I thought maybe that was the inspiration for the marking.) But I can't do it: the last character looks to be an "X, not an "N."
This boxy unit had just been used in the previous episode ("Court Martial")--in both Commodore Mendez' office and in the courtroom. So for "The Menagerie," they tried to make it look like a third, different unit by redecorating it with all the goofy wording. (The wording still remains on the unit when we see it again down on Eminiar in "Taste of Armageddon.")
Pretty much everything you would want to know about the various desktop boxy computer units can be found here:
http://tosgraphics.yuku.com/topic/371/t/TOS-Computer-props.html