Two arms are linked by a two-leaf flat hinge. Each has a linear scale  to 300, divided to 10, subdivided to 2 with alternate mirror gilding and to 1, numbered by 10. The 'baseline' arm has the final subdivision not on the edge but to coincides with the index of a sliding mount for the third arm, which moves on a pivot carried by this mount and with the same scale extended to 430. The final division to 1 on the arm on the fixed pivot is on the horizontal face of a right-angle edge; for the arm on the sliding pivot, the division to 2 is on a bevelled face, while that to 1 is on a final short vertical edge, so as to be able to define precisely the intersection of the two pivoted scales. Each arm has two blued-steel sights: two slit sights on the baseline arm, one slit and one upright plane sight on the pivoted arms.
Underneath the baseline arm is a scale of 12 inches 'EIN SCHVCH', the first inch, marked 'ZOLL', is undivided, subsequent inches are divided to 2, 3, 4, etc parts to 12, numbered by 1. Signed: 'Iost B[ubar]rgi F' and engraved with the name of an owner 'Alberto Marchoni'
Underneath the arm on the fixed pivot are three gunnery scales, 'STEIN', 1 to 60 decreasing, divided to 5, subdivided to 1, numbered by 5; 'GOSSEN EISEN', 1 to 125, similarly divided; and 'BLEI', 1 to 125 decreasing, similarly divided. A short fourth scale is partly covered by a brass end piece.
See: B. Bramer, Bericht zu M. Jobsten Burgi seligen geometrischen triangular Instruments (Kassel, 1648) and J. Bennett and S. Johnston, The Geometry of War 1500-1750 (Oxford, 1996).