PLATO: How an educational computer system from the ’60s shaped the future.

This line printer was incapable of shifted characters, so the ^ indicated a shift (^7 would be apostrophe on the common non-Selectric keyboards of the day, for example, and ^/ would be a question mark). Infamously, PLATO Notes even inspired early consternation over network censorship during Watergate when the NSF got wind of a Notes discussion about President Nixon's possible impeachment and promptly called Bitzer (“We just got a call from Nixon’s office. The White House says that our money will disappear if this goes ahead, and we know you’ll disappear...”). Bitzer required the student who started the discussion to post a disclaimer that “it is not permissible in the classroom or on PLATO to organize political mobilization.”

Relevant: Paul Tenczar and TUTOR.