The interviewer drew a top and side view of the “home screen”, circular button on the front of an iPhone. If the critical features of the button are the diameter and the position/width of an anti-rotational feature (which was drawn in one of the views), where would you place your datums and critical dimensions. Why? How do you define the datums to reduce the gap and offset between the button and the glass, and the tilt of the icon with respect to the glass?