Signed: ADescrolieres facie 1579
The three arms, each with a pair of sights, move on a single pivot and as they do so a cursor, connected to both outer arms, moves along the central arm, which is marked with a degree scale, indicating the angle between the outer arms, and with the number of sides of the regular polygon formed by repeating this angle. One of the outer arms bears the maker's signature, the other is engraved 'Pro declinatione muri', since these arms indicate the angle by which the walls of the fortification decline from each other. If the sights on the central arm are trained on the centre of the polygonal structure, those along the outer arms give the directions of the walls. A pin beneath is for mounting the instrument on a staff or tripod.
Length folded: 190 mm
Lewis Evans Collection
Inventory no. 36,261