A method of expanding the on-track operational range of a disk drive based upon detection of an external vibration condition. The decelerating device has at least one secondary stop, which rotates in the same direction as the gripper drum, has a slower speed than the gripper drum for slowing down the printed sheets, and on which the printed sheets are slowed down upstream of the stop. The first feed screw and the second feed screw are coupled to the at least one outer hub. The metrology tool compares its empirical measurements to the predicted measurements in the library. The insert and wall include tenons and grooves to secure the insert in the housing member. Accordingly, a blur threshold value is determined for the wearer according to a blur perception criterion that varies based on an optical-power addition value prescribed for the wearer.