An alidade or sighting rule would generally be considered one of the more ordinary and mundane of surveying instruments but here, through elegance of design, gilding and fine decoration in a manner typical of Erasmus Habermel, it has been made into a beautiful object.
The addition of a magnetic compass with a carefully divided scale based on the 32 compass directions, means that the instrument could be used for taking angles as well as for simply marking directions on a sheet of paper supported on a plane table.