To determine the type of interference at a point on the viewing screen, which is done? We pair the ray from the top of one zone with the ray from the top of the adjacent zone and then determine their path length difference. We pair the ray from the top of one zone with the ray from the bottom of the adjacent zone and then determine their difference in angle to the point on the screen. We pair the ray from the top of one zone with the ray from the bottom of the adjacent zone and then determine their path length difference. We pair the ray from the top of one zone with the ray from the top of the adjacent zone and then determine their difference in angle to the point on the screen.