A comparison of three methods for determining the reading addition.

Three subjective determinations of the reading addition required by each of 10 subjects were obtained in this study with the use of a cross cylinder grid target, a variable color, near-point, grid target and an ordinary reading card. All three methods gave similar results. In addition, there was no change in the measurement when the color of the horizontal and vertical lines was reversed on the variable color, near-point, grid target.