PLEASE PLEASE an Undo

[luisphysics]

OMG please please I would love to have a few undo for the input line on either home and CAS. I was just plugging in a rather complicated formula with units and I stinking pressed Shift+Esc BUT I was trying to press the SHIFT+USER button and I failed. This one feature should honestly be like top priority above anything. Granted I should know how to do unit analysis and I do, but I get lazy sometimes or as in this case I want a sanity check(since I'm tired and stressed) from something I trust.

For now I will just suffer.