The instrument consists of a circular brass plate with a compass and alidade.
At the circumference of the circle is a scale of degrees 90 to 0 to 90 to 0 to 90, divided to 5 and 1 (with alternate cross-hatching), and numbered by 5. Inside the degree scale is a circular scale of the points of the compass, with 32 points named in Dutch, and with each interval subdivided into 2 and 12 parts (with alternate hatching).
An area at the edge of the plate between north-east and north-north-east has been repaired and re-engraved.
Within the direction scale is a double shadow square, each of whose sides runs 0 to 60, divided to 10 and 2 (with alternate hatching), and numbered by 10. The date 1565 appears in scrollwork between the shadow square and the south direction.
Inset into the plate is a compass bowl 175 mm in diameter. There is a meridian line and a target line for magnetic variation which is engraved in the form of a needle, similar to but not identical with the needle mounted above it.
There are four fixed sights riveted at the edge of the plate, one for each of the cardinal directions, forming a surveyor's cross or square.
The alidade with its pair of sights is a replacement and is engraved with the chronogram 'DeLIneaVIt refeCItqVe MICheL brVXeLLIs' for the year 1930.
The instrument can also be used to measure vertical angles and it is provided with a shackle and suspension ring at the south point.
The reverse of the plate has a large central threaded socket to attach the instrument to a staff or tripod.
See: J.A. Bennett, The Measurers: a Flemish Image of Mathematics in the Sixteenth Century (Oxford, 1995), catalogue no. 32.
Provenance: Henri Michel Collection; Billmeir Collection (accession no. 57-84/125)