The sliding guides for the accessory frames are equipped with a screw and a spring for fine adjustment, within approximately one centimetre, of the height of the accessory being used.
In one of the cursors, the pin on which the plates are fixed is on a sliding guide allowing horizontal movements normal to the graduated rod of up to 2.5 cm.
This cursor is indispensable in the interference experiment with Fresnel mirrors lenses in order to arrange them in such a way that the incidence is almost grazing.
Originally, the apparatus was illuminated by solar light by placing a cylindrical lens or slit, or even a round opening, at the head of the bench; observations were carried out by means of a special eyepiece. Later, artificial light sources of monochromatic or white light of sufficient intensity were used and the interference or diffraction figure was projected onto a screen.
Since 1965, an He - Ne laser has also been used as a light source.