Bramer describes a triangulation instrument whose design he attributes to the instrument maker and clockmaker Joost Bürgi, who was employed by Tycho Brahe. Books explaining the use of such devices are not uncommon in the period, even though the instruments themselves are rare. They are always presented as universal in their applications, among which military uses are given prominence.
In figure 68, Bürgi's instrument is shown used by gunners on a rampart overlooking an estuary, beyond which a company of foot soldiers advances on an undefended fort. A baseline is measured between the two positions of the instrument, the sliding pivot of one sighting arm is adjusted so that the distance between the pivots is a scaled representation of the baseline, and sights are taken from both positions. The sides of the triangle on the ground - similar to that formed by the instrument - are then found by applying the scale to the intersection readings of the pivoted arms.