When closed this instrument resembles a large pair of compasses, with flat limbs inscribed on all sides and a highly decorated hollowed joint. One limb has foldable sights on the outside edge, one of which is missing.
When fully opened to 90?, further plates, two skeletonized folding geometrical squares and a third arm with a fiducial edge a folding sight with a spike can be folded out from inside the hollow limbs. Even in the upright position, this sight slides into a slot in the upper side of one limb. A second sight arranged in the same way is broken off.
A movable ring around the joint with a small hole suggests that a plumb bob was fitted to the instrument.
In contrast to the scales found on other Humphrey Cole instruments, those found here are inaccurately engraved and laid out.
On one limb a 9 3/4 inch scale, numbered by 1. Each section is divided to 32 parts and consecutively numbered by 4 up to 312.
On the edge of this limb and on the face and edge of the other limb are the scales usually found on folding rules for calculating areas and volumes.
A scale for board measure, marked 'Borde measure', and a scale for timber measure, marked 'Tim measure'. The board scale runs from 13 to 36, the timber scale from 13 to 36. Both scales are supplemented by scales providing the board and timber measures from 1 to 11 inches, but in this case only represented by plain boxes.
Over both legs a list of cannons 'The Names of Ordenan', the weight of every cannon 'H Much euery pece wayeth', the diameter of the barrel 'H Hie die piece is in the mouthe', the diameter height of each bullett in inches 'H Many Inches hie the bullett is', the amount of powder needed for each shot in pound 'H many lb of powder euery pece shot', and how many pounds each bullet weighs 'H Many pou<n>de euery shote wayeth'.
The 'Basilisco', normally to be found in Cole's list, is not named, although there is space for more entries in the list.
Below this list on the left limb on its face and edge is 'The table of timber measure' in feet, inches and fractions of inches.
Inscribed on the left-hand column beneath the figures is the inscription 'SQVARE YNCHES OF THE TYMBRE'.
The signature and the date 'Humfray Coolle Mad This' are below this list close to the pointed ends of the limb.
On the face of the other limb are scales for the conversion of measures in Latin, titled 'DE PARTUBVS MENSVRAE SEV SPECIEBVS GEOMETRIAE PRACTICAE', as follows: 'Granu<m> igitur hordei, est minima me<n>sura', 'Digitus habet 4 grana per latera contigue disposita', 'Vncia habet 3 digitos', 'Palmus habet 4 digitos', 'Dichas habet 2 palmos', 'Spithama habet 3 palmos', 'Pes habet 4 palmos', 'Sequipes habet 6 palmos', 'Gradus habet 2 pedes', 'Passus simplex 2 pedes cum dimidio', 'Passus Geometricus quo Vtitur', 'Cosmometra habet 5 pedes', 'Pertica habet 10 pedes', 'Cubitus habet 6 palmos', 'Stadium habet 125 passus', 'Leuca habet 1500 passus', 'Miliare Italicum habet 1000 passus', 'Miliare Italicum habet 8 stadia', 'Miliare Germ cont 4000 passus', 'Miliare Ger magnum 5000 passus', 'Miliare Germ com<m>une 32 stadia'.
When the limbs are completely opened, two folding quadrates are fully spread.
The larger one is marked with a shadow scale inscribed 'Latus Vmbrae Rectae' and 'Latus Vmbrae Versae' with two different scales: one 0 to 60 to 0, the other 0 to 45 to 0. Both scales are numbered by 5 and divided to 1. The same scales are inscribed on the other side, but not labelled.
The smaller quadrate has a scale 0 to 90 and 0 to 45 on one side and a scale 0 to 90 on the other side.
The instrument was presented by Augustus Meyrick in 1878 and is described and illustrated in R. T. Gunther, "The Great Astrolabe and other Scientific Instruments of Humphrey Cole", Archaeologia 76 (1927), pp. 273-317, esp. pp. 294-6; F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), p. 105, no. 311; S. Ackermann, Humphrey Cole: Mint, Measurement and Maps in Elizabethan England (London, 1998), pp. 80-2, no. 22.