Most of the light will refract at the same angle \(\alpha\) that it was incident on the ruler so we will be able to establish our S₀  bright spot with this knowledge. Angles \(\alpha\) and \(\beta_n\) will need to be determined using the length L to the wall and another length \(l_n\), that will be the length from the central line to the each bright spot S_n . The central point can be generated with some careful consideration of the reference beam and the location of S₀ . It may be best to measure each point S_n from the reference beam and then subtract the extra distance later.

The equation that we use to generate the wavelength can be made with some consideration of how the laser illuminates the ruler.