For the wavelength measurement using a two-beam Fizeau interferometer an accuracy of about 2 parts in 107 is claimed. To reach this limit the influence of error sources has to be minimized. A discussion of error sources impairing the obtainable accuracy will be given in this paper.
"Error Sources In Fizeau-Interferometric Wavelength Measurement", Proc. SPIE 1121, Interferometry '89, (3 April 1989); doi: 10.1117/12.961250; https://doi.org/10.1117/12.961250