Honestly curious - what kind of abuse could cause a calibration error?
My kids abuse my iPad pretty heavily but generally smacking on the screen with their hands and fingers a lot but I still have never seen it mis-calculate a touch.
iPads used capacitive touchscreens which aren't prone to the same sorts of calibration issues that resistive touchscreens are.
I don't know much about electronic voting machines but I wouldn't be surprised if they mostly used resistive touchscreens (which are historically much cheaper to produce).
My kids abuse my iPad pretty heavily but generally smacking on the screen with their hands and fingers a lot but I still have never seen it mis-calculate a touch.