Since it is quite difficult the centre the telescope in this way, by leaving the staff free, it can be positioned so that the point to be sighted falls near the centre of the reticle and then, once the staff and the slide have been blocked, they are moved slightly up or down with the micrometric screw that connects the cursor to the slide until the point to be sighed is at the centre of the reticle.
The scale, graduated in millimetres (length 113 cm) is etched into a strip of silver inserted into the shaft between the two guides of the cursor; the index and a fifty thousandth vernier are etched on one side of a window in the cursor under the telescope, while on the other side there is an eyepiece with a guide that allows reading.