Table 2.

Summary of magnifier movement parameters: navigation errors

Parameter	Description
Pauses	A period of at least 2 seconds where the magnifier remained stationary in the X-plane during the forward or retrace movement across a line
Regressive movements	Movements (≥ 5mm) in the X-plane in the opposite direction to that in which the magnifier should have been moving in the forward or retrace phase.
Overshoots	Movements in the X-plane where the magnifier was moved too far beyond the end (forward phase) or start (retrace phase) of a line and there was a compensatory movement (≥ 10mm) in the opposite direction to bring the magnifier back to the correct X-position.
Undershoots	Movements in the X-plane which were not sufficient to bring the magnifier to the end (forward phase) or start (retrace phase) of the line and a compensatory movement (≥ 10mm) in the same X-direction had to be made
Vertical corrective movements	Movements primarily in the Y-direction of greater than 3mm that corrected an error in the vertical positioning of the magnifier.