A RARE PERSIAN GUNNER’S CALIPER PRODUCED FOR THE PERSIAN ARMY, DATED 1154 AH/1741-42 AD

A very rare 18th century Persian gunner’s caliper (also known as gunner’s compass/ gunner’s sector) modelled after one of the various types of gunner’s calipers developed and produced in 18th century England. Despite the fact that English versions of this instrument are quite common, eastern versions seem to be very rare, since there are very few descriptions or references to similar instruments in literature. The Persian caliper at hand seems to be identical to an English gunners caliper auctioned 30th of October, 2019 at Morphy Auctions, as lot. 1187, made by “Gilkerson Tower Hill London”. A quick comparison shows that the numerical tables and engravings correspond almost identically.
The instrument consists of two thin legs or rulers, pivoted with a screw and movable around the screw. Both arms are rounded around the screw. The instrument is engraved on both sides.
The arms on the screw side of the instrument are engraved with scales for measuring lengths and diameters in inches and a tables indicating the amount of gunpowder quantity needed for proof and service for various diameters of brass mortars and howitzers for both sea and land. The screw side also has circular scale for measuring the diameter of bores in the round section.
The reverse of the instrument contains two tables for artillery: one for brass guns on the upper leg and one for iron guns in the lower leg with two rows of numbers. The Persian captions indicating the tables are textually longer than on the English instrument. For example the caption “proof” on the English instrument becomes “gunpowder weight for testing the cannon” on the Persian instrument.
The only inscriptions which are different from the European original are both on the reverse side: (1) the date above the pivot, which reads 1154 (AH) and (2) a vertical inscription indicating “the property of God” left to the pivot.
17.7 cm. length

CATALOGUE NOTE
The gunner’s caliper is a modification of the sector for the use with artillery. The major modification is that the two arms have been hollowed out slightly to allow the user to measure the diameter of canon balls (convex diameter). Most gunner’s calipers also allowed to user to cross the arms over top of each other to measure the diameter inside the mouth (bore) of a cannon.
The arms were usually engraved with various scales and tables such as : scales for concave and convex diameters, degrees and tables for weights of iron shot diameters. This caliper is clearly modeled after 18th century European models

LITERATURE
J. Robertson, A Treatise of Such Mathematical Instruments as are usually put into a portable case containing their various uses in arithmetic, architecture, geometry, surveying, trigonometry, gunnery etc., London, 1757
M. Williams and E. Tomash, “The Sector: Its History, Scales, and Uses”, IEEE Annals of the History of Computing, vol. 25, no. 01, pp. 34-47, 2003.
David S. Weaver, “The English Gunner’s Caliper”, Arms Collecting, Vol. 33, No. 4, pp.
Morphy Auctions Catalogue, 30th October, 219. Lot 1187: FINE SET OF ENGLISH BRASS ARTILLERY CALIPERS.