example the remaining positive test area is the entire area the positive test area is then divided into multiple segments in this example the positive test area is divided into two segments the first of the two segments is displayed to the user in fig2 b the user would respond in the affirmative that distortion is present in fig2 b the segment shown in fig2 b would be kept in the test area the grid i e the other of the segments in fig2 c would then be presented to the user the user would answer in the negative because no distortion is present the test area in fig2 c would be removed from the test area next the remaining test area would be calculated and split into two segments the two segments of the remaining area illustrated in fig2 d and 2e are presented to the user the user would answer in the affirmative that distortion is present on both fig2 d and 2e the remaining test area then includes the segments shown in fig2 d and 2e each of the segments is divided into two leaving four segments to be tested the program can determine an efficient way to present the four segments for example the program can assume that the distortions are continuous and potentially overlap the intersection of the test grid segments illustrated in fig2 d and 2e as a result the segments presented in fig2 f and 2g are the segments that do not include the area where the segments.