The outside on the top leaf is laid out as a nocturnal consisting of two circular scales and two volvelles one of which has an index. The outside scale is marked with the usual Latin names (some abbreviated) of the zodiacal signs (numbered 1 to 12 beginning with Aries) and their symbols. Each sign has a 30? scale, numbered by 10 and divided to 2 by alternate shading.
The inner scale is marked with the usual Latin names of the months and the corresponding number of days, numbered by 10 and divided to 2 by alternate shading. The top centre of the instrument corresponds to circa 18 April. The equinoxes correspond to 11 March and 14 September, the solstices to 12 June and 12 December.
The outer volvelle, labelled 'The nighte houres', has an hour scale marked anticlockwise 4 to 12 to 9. The hours are further indicated by small teeth, an index for 12 o'clock is decorated with a sun effigy.
The central disc is marked 'THE POLE STERRE'. The index for alignment with the pole star is decorated with a moon effigy. The area around the central hole is decorated with a sun burst.
The inside of the upper leaf is marked with a list of latitudes in five concentric rings with eight entries each; a sixth central ring is inscribed 'The latitudes of all the principall townes and cities of evrope'. The following towns are named: 'Edenboro 57 0'; 'Co<m>postel 44 20'; 'Lisbona 39 38'; 'Barsalo 41 35'; 'Na<n>tes 48 12'; 'Parisius 47 55'; 'Marsilia 43 6'; 'Tolosa 43 30'; 'Louani 50 58'; 'Rone 49 0'; 'Antwerpia 51 28'; 'Bruxella 51 0'; 'Brugae 51 30 51 30'; 'Gand 52 24 51 24'; 'Tor a c 51 40 51 40'; 'Francopho 50 12 50 12'; 'Cracouia 51 0'; 'Dantis c 55 0'; 'Lubecu<m> 54 48'; 'Emde<n> 53 42'; 'Constanti 43 0'; 'Florentia 43 4'; 'Neapolis 41 0'; 'Venetia 44 50'; 'Roma 41 50'; 'Douer 51 0'; 'Exiter 51 0'; 'London 51 34'; 'Oxford 51 50'; 'Bristo 51 0'; 'Northampt 52 50'; 'Norwiche 52 30'; 'Harford 52 50'; 'Leisetr 52 50'; 'Noting 53 0'; 'W Chester 53 10'; 'Linckoll 53 15'; 'Yorke 54 0'; 'N cast 55 0'; and 'Barwic 56 50'
A universal equatorial sundial is hinged between the upper and lower leaf of the compendium.
The hour circle is mounted on a crescent shaped support, so that it can be rotated. One side is marked with a 24-hour scale, numbered twice I to XII and divided to 1/2 hours. The other side for use in winter is marked for 12 hours, numbered VI to XII to VI and divided to 1/2 hours.
The signature of the maker and the date 'Humfrey C?le 1575' are engraved on this side of the hour ring.
Fixed to the hour ring is a skeletonised latitude quadrant with a degree scale 0 to 90, numbered by 10 and divided to 2. The edge at 90? is extended to form a pin gnomon. The latitude quadrant slides into a notch in the supporting crescent which enables the dial to be set for the appropriate latitude. A plumb bob originally fixed to a hole in the apex of the quadrant is now missing.
A magnetic compass with a painted compass card in gold, green, grey and burgundy is set into the inside of the lower leaf. Thirty-two points are indicated with the eight main points marked in full, the others marked with their first letters 'NORTH', 'NBE', 'NNE', 'NEBN', 'NORTH EAST', 'NEBE', 'ENE', 'EBN' etc. North is further indicated by a fleur-de-lis, east by a cross, south by an arrow and west by a spade.
The outside of the lower leaf is laid out as a perpetual calendar with Saints days, Christian feasts, Dominical Letters, Golden Numbers and Epacts, consisting of seven circles and titled in the centre 'THIS TABLE BEGIN<N>ETH AT 1572 & SO FOR EVER'.
The three outer circles give the dates of 38 saint days and Christian feasts. The following dates are given: 'I 1 Circ 6 Epiph 13 Hill 25 Co Pau'; 'F 2 Puri Ma 16 Val 25 Mat Ap'; 'M 12 Grego 25 Ann Ma'; 'A 4 Ambro 23 George 25 Marcus'; 'M 1 Phi Iac 6 I Ev 26 Augus'; 'I 11 Barn 24 I Ba 29 Pe Pa'; 'I 2 Visi Ma 22 Ma Mag 23 I Ap'; 'A 1 Pi Vi 10 Lau 24 Bar 29 De Io'; S 8 Nat Ma 21 Mar 29 Mic'; 'O 13 Edwa C9 18 Lu 28 S Iude'; 'N 1 Om S 2 Om An 30 Andr'; 'D 6 Ni 8 C9 21 Th 25 Na'.
The two circles in the middle give a list of Dominical Letters for ordinary years and leap years ('DO LE' and 'LE Y') starting with 'F / E' and running clockwise to G.
The two circles in the centre are marked with tables for the Golden Numbers ('PRI') and the corresponding Epacts ('EPA') as follows: '15 15'; '16 26'; '17 7'; '18 18'; '19 29'; '1 11'; '2 22'; '3 3'; '4 14'; '5 25'; '6 6'; '7 17'; '8 28'; '9 9'; '10 20'; '11 1'; '12 12'; '13 23'; '4'.
The outer rim is engraved as follows: 'AS TIME AND HOVRES PASITH AWAYE SO DOETH THE LIFE OF MAN DECAY' and 'AS TIME CAN BE REDEMED WITH NO COST BESTOW IT WELL AND LET NO HOWR BE LOST'.
The rim is decorated with a rope-twist design. The suspension consists of a sphere supported by two scrolls with an inset ring through which passes a loose ring.
The instrument retains its original fitted brown leather case stamped in gold and lined with red velvet.
The instrument was bequeathed by Octavius Morgan in 1888 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. 289-91 and figures 34-5; F. A. B. Ward, A Catalogue of European Scientific Instruments in the Department of Medieval and Later Antiquities of the British Museum (London, 1981), pp. 125 ff., no. 360; and S. Ackermann, Humphrey Cole: Mint, Measurement and Maps in Elizabethan England (London, 1998), pp. 59-61, no. 12.