We have developed an interferometer for gauge block calibration based on phase shifting algorithms. The measurement process can provide flatness, parallelism, and length. Wavelength values need to be corrected according to the refractive index of air. This correction is obtained indirectly using Edlén’s equation. High-resolution sensors provide the temperature, pressure, and relative humidity readings. To preserve stability, the interferometer is encapsulated in a chamber with active temperature control. Its design, measurement principle, calibration, stability, and reproducibility are analyzed. Since one goal is to employ robust and cheap diode lasers as light sources, we describe the system developed to stabilize a red laser diode using a mode locking technique with a reference gas cell. The instruments and assembly are used to avoid the Doppler effect in the gas cell, which would limit wavelength resolution. Several experiments are carried out to restrict the influence of environmental changes, which affect laser diode frequency.