Okay, at work someone dun goofed with the adding machine switches.
In my attempts to feed the horse salt (never mind what that means, or maybe you can figure it out) and wedge these switches to fixed/immovable positions... I come to this switch.
Off | Σ On
I've tried to Google what this switch/function is for, but I can't find anything... Or, what I do find gets into some complicated (to me) hullabaloo with a whole lot of other symbols/functions that have nothing to do with an adding machine.