A laser beam with a wavelength of 524 nm is exactly perpendicular to a screen having two narrow slits spaced 0.150 mm apart. Interference fringes, including a central maximum, are observed on a viewing screen 1.05 meter away. The direction of the laser beam is then slowly rotated by 1.00 degree around an axis parallel to the slits until it makes an 89.0 angle with the screen.