The Plus box in the Surface Profile dialog box (Insert | Dimension | Profile | Surface) enables you to enter a tolerance value along the plus direction. This means that any profile that measures more than your nominal or theoretical profile can still be a valid measurement as long as it falls within the tolerance range specified.
PC-DMIS also allows a negative-upper tolerance (or a minus tolerance in the positive range). This is done by entering in a minus sign before the value in the Plus box.