Because in vision screening, only a limited number (e.g. eight or
four) of equidistantly distributed orientations are required, the
pointing orientation may occur within a tolerance, which depends
on the number of orientations to be discriminated. The tolerance is
expressed as the angle of the sector originating at the central LED
(Fig. 2) and having an angle bisector crossing one of the target LEDs
(Fig. 2). If, for instance, the vision test requires the participant to
discriminate between eight orientations, the angle of the sector subtends 45. All pointing orientations with a deviation of