Theoretically, it has no effect. Because r = (dm 2-dn 2)/4 (m-n) wavelength in the formula, if the chord length L is measured, (d/2) 2 = (l/2) 2+d 2. D is the distance from the chord to the center of the circle. When calculating r, the term about d is just eliminated, and the difference in diameter is just equal to the difference in chord length, so it does not affect the calculation result.