[IIsi50MHz]

And in my experience ties in nicely with the fact that when a dumb terminal glitched or lost sync with the server, control codes would start to litter the screen instead of being interpretted. You'd see things like:

…thsi typo^Ŵ^H^H…

start to appear, sometimes followed by several random letters hit in frustration, before the final hard-reset of the terminal and resignation to the fact some unsaved work has been lost.