Once the telescope (or graduated disk) has been blocked on the axis of the instrument, the sighting is adjusted by means of a micrometric screw prior to reading on the two verniers to improve accuracy of the measurements; the combination of the readings made on the two verniers, since these are diametrically opposite, any alidade eccentricity error is eliminated.
The collimator is composed of a vertical slit, with an adjusting screw, placed on the front focal plane of a converging collimating lens.
By illuminating the slit with a light source placed along the axis of the collimator, the collimating lens generates a parallel beam of light which the objective of the telescope makes converge on its own back focal plane, thus producing an image of the slit which the eyepiece, which lies on that plane, allows us to view.
The platform consists of two superimposed disks and can be fixed to the axis of the instrument; one of the two disks lies on the other by means of two projecting screws and a pin with a spring. They are equidistant and can thus be arranged perpendicular to the instrument axis. ...continues