On the outside it is marked with a table with Saints' days and Christian feasts, planetary aspects, zodiacal and calendrical scales and a list of latitudes, which is continued on the outside edge.

In use the pin hole would be set to the appropiate time of the year and the right latitude on the analematic scale on the inside.

The outside of the ring is marked anticlockwise with several scales as follows (starting at the top):

1) Table of Saints' days and Christian feasts (as well as the beginning and the end of the dog days) corresponding to the calendrical scale. The following dates are given: for January, '1 CIRCV 6EPIPH 13 HILA 25 Co Pa'; for February '2 PVRIFI MARI 14 VALE; 4 MAT'; for March '12 GREGORI 25 ANVN MAR'; for April '23 GEORGE 25 MARCVS'; for May '1 PHILLI IACO 6 IOAN EVAN'; for June '11 BARN 24 IO BAP 29 PETER PAVL'; for July '6 DOGE BEGIN 22 MAG 25 IA APO'; for August '1 PE VIN 17 DOG EN 24 BART 29 DEC IO'; for September '8 NATI MARI', '21 MAT 29 MICH'; for October '13 EDWARD CON 18 LVC 28 SI IVD'; for November '1 OMNI SAN 2 OM AN', '30 ANDR'; for December '6 NICO 8 CON MA 21 THO 25 NAT DO'.

2) A movable band is engraved with planetary aspects in words and symbols: 'CONIUNCTION' 'SEXTILE' 'QVADRINE' 'TRINALL' 'OPPOSITION' 'TRINALL' 'QVADRINE' 'SEXTILE'. A boss in the shape of a lunar crescent aids manual rotation.

3) A fixed band is engraved with a zodiacal scale with the usual Latin names (indicated with the first letter) of the signs and their symbols . Each sign has a 30? scale, numbered by 10 and divided to 2 and 1.

4) Another movable band, with a boss to aid manual rotation, is inscribed with the age of the moon, numbered 1 to 29.

5) A fixed band is engraved with a Julian calendar scale with the usual Latin names of the months (indicated by their first letter). Each month has a corresponding date scale, numbered by 10 and divided to 2 and 1. December appears to 31.25 days to indicate the leap year.

The equinoxes correspond to 11 March and 14 September, the solstices to 13 June and 12 December.

6) A third movable band with a pin hole has a list of cities with their latitudes (anticlockwise starting at the pinhole): 'Notingame 53', 'Leiseter 52 50', 'Harford 52 50', 'Norwiche 52 30', 'Northampton 52 50', 'Bristo 51 20', 'Oxforde 51 50', 'London 51 34', 'Exiter 51 0', 'Dover 51 0'. This list is continued on the outside edge:'Linckolne 53 15', 'West Chester 53 10', 'Louanium 50 58', 'Antwerpia 51 28', 'Winchester 51 0', 'Saulisburie 51 15', 'Barwick 56 0', 'Newe Castell 55 0', 'Yorke 54 0'.

On the inside of the ring are two circular perpetual calendars consisting of two circles each. Both are marked 'THIS TABLE BEGINETH AT A 1575 AND SO FOR EVER' in the centre. One calendar gives a list of Dominical Letters for common years and leap years, the other gives the Golden Numbers and Epacts as follows: '18 / 18' '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' '14 / 4' '15 / 5' (recte 15) '16 / 26' '17 / 7'.

Next to the latter is a scale with lines for the zodiacal signs (indicated by their symbols) for every 6? and latitude lines for latitudes between 50? to 56? .

The signature 'H C?le' appears at the bottom of this scale.

Next to this scale is a table for the entry of the sun into a particular zodiacal sign. The months are indicated by the first letter of their names, the sun by its effigy twelve times and the signs by their symbols. The columns are headed 'M' for the months, 'D' for the dates, 'So' for the sun, and 'Si' for the signs. The following values can be read off:

The following dates can be read off: 11 January / Aquarius, 10 February / Pisces, 11 March / Aries, 11 April / Taurus, 12 May / Gemini, 13 June / Cancer, 14 July / Leo, 14 August / Virgo, 14 September / Libra, 14 October / Scorpio, 13 November / Sagittarius, 12 December / Capricorn.

The date given for the sun's entry into Cancer deviates from Cole's usual date 12 June.

Next to this table are oblique lines for the common hours numbered 4 to 12 to 9, and the lines for the latitudes between 50 and 56 .

The instrument was presented by C. J. Wertheimer in 1905 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. 291-3. See also 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. 61 ff., no. 161 and S. Ackermann, Humphrey Cole: Mint, Measurement and Maps in Elizabethan England (London, 1998), pp. 45 ff., no. 8.