PASCO make a set of slits with different width and spacing.On this disk are two inclined slits (variable double slit).Measuring the fringes is difficult as they are quite close together. Using a much longer distance than the optical bench helps but the pattern gets a bit fuzzy, how about taking a photo? The angle isn"t easy either.The line won"t go through the origin because you won"t be starting at the end of the triangle.