A sector-shaped plate comprising about 130 degrees has a degree scale on the limb 0 to 122, divided to 5, subdivided to 1, numbered by 5, and outside the scale is the inscription 'INSTRVMENTVM PER CIPIENDI DISTANTIAM PER SVPERFICIEM'. The rest of the plate is filled with decoration of exotic creatures, leaves and strapwork. At the apex of the sector is a 3-element compass hinge where a long arm fixed to and extending beyond one edge of the plate meets a short pivoted arm that reaches only to the limb, with a wing-headed clamping screw moving in a slot cut as an arc in the plate. At the end of this short arm is a 2-leaf compass mount, on which pivots a second long arm. Both long arms have pairs of sights, and have scales 0 to 44, divided to 1, subdivided to 1/5 and 1/10, numbered by 1; on the fixed arm the subdivision is on the face, on the pivoted arm it is on a bevelled edge: this allows the intersection to be noted precisely on the scales. The short arm, which acts as the baseline, has a scale [0] to [10], divided to 1, subdivided to 1/2, numbered by 1. The underside of the plate has three mounting sockets.
