The prismatic circle, a sextant-like instrument, was made in the 1850s and is one of the oldest instruments in the University of Ljubljana, Faculty of Civil and Geodetic Engineering collection. It measures the angle between the Sun and the horizon, and with additional data from the almanac and a known instant of the Sun's position, the geographical position can be determined. It is held with a wooden handle when taking measurements. The vertical circle has a sexagesimal division engraved on a silvered metal bracket with intervals from 0° to 130° and from 180° to 270°. The reading is done by the two verniers on either side, the unit of the vernier being 20''. The smaller telescope with a Ramsden retractable eyepiece and a 6 mm objective provides a more precise sighting of the target point.

The instrument was completely restored in 2017.