A fixed wavelength absolute distance interferometer including a first interferometer comprising a first light source transmitting a first light beam having a wavelength W toward a measurement target, a wavefront radius detector configured to provide a first measurement responsive to the wavefront radius at the wavefront radius detector, and a first path length calculating portion calculating a coarse resolution absolute path length measurement R; and a second interferometer comprising a beam transmitting device transmitting a second-interferometer light beam having a wavelength Λ, a beam splitting/combining device separating the second-interferometer light beam into reference and measurement beams and combining the returning reference and measurement beams into a combined beam, a second-interferometer detector configured to receive the combined beam and provide signals of a phase φ of the combined beam, and a second path length calculating portion configured to determine a medium resolution absolute path length measurement ZM.