The outside of the cover of the instrument is laid out as a nocturnal consisting of a fixed circular scale and a movable disc. The fixed scale is marked with the names of the months in English as 'Ianneuarie, Februarie, March, Aprill, Maie, Iuune, Iulie, August, September, October, Nouember, December', and the corresponding number of days (May has only 30 days), numbered by 10 and divided to 1.
The disc has a 24 hour scale, marked twice I to XII. The hours are further indicated by teeth with a longer index at 12 o'clock. The centre of the disc is decorated with foliate scrolls.
The index which would be aligned with the pointer stars is missing and has been replaced by a small pointer fixed with a plate to the centre, thus making it impossible to use the instrument properly.
The centre of the inside of the cover is engraved with the arms, crest and motto of Robert Devereux, Earl of Essex (died 1601). It is surmounted by a crown and encircled by the motto ' HONI SOIT QVI MAL Y PENSE' and the words 'INVIDIA VIRTVTIS COMES'. Further to the outside are the names and latitudes of 39 towns in four concentric circles as follows (clockwise): 'London 51 33', 'Briscils 44 5', 'Patavia 44 28', 'Burdensi 45 30', 'Norinbarg 40 24', 'Constantinople 43', 'Alexandria 43', 'Ierusalem 36 40', 'Edenburge 57', 'Venice 45 18', 'Perusia 42 30', 'Brasilia 47 41', 'Burgis 42 48', 'Antioch 37 20', 'Corinth 35 55', 'Cesaria 31 40', 'Florence 45 40', 'Napels 40 36', 'Orleance 47', 'Viena 48', 'Perusia 42 30', 'Athens 37 15', 'Niniui 41 40', 'Babilou 35', 'Roome 44 40', 'Paris 48 30', 'Lions 45 10', 'Ments 50 8', 'Braga 43', 'Granata 37', 'Da<m>ascus 33', 'Lisbon 39 38', 'Malta 34', 'Compostella 42 15', 'Carthage 38', 'Heercules pillers 36 15', 'Tours 47 30', 'Antwerp 51 28', 'Quinsey 37 40', and 'Cuba 231/2.'
A magnetic compass with a painted compass card in gold, blue, grey and burgundy is set into the base of the instrument. Thirty-two points are indicated with the eight main points marked in English in full, the others marked with their first letters. North is further indicated by a fleur-de-lis, east by a cross, south by an arrow and west by a spade. A degree scale on the brass ring surrounding the compass is marked 0 to 360, numbered by 10 and divided to 5 and 1.
The base itself has a list of ports and harbours grouped by compass directions:
'S E B S N W B N', 'LENOIS', 'DEEP LVX', 'WITHIN THE NEEDLES OF WIGHT'
'S S E N N W', 'SAIN HEAD', 'BOLLAINE', 'HARWICH', 'LESTOF BEFORE THE FEN'.
'S B E N B W', 'WINCHESTER', 'CAANE NOR<M>AN', 'MARGREAT', 'ORFVRD BEFOORE WIGHT', 'CALLIS'.
'N B E S B W', 'FLVSHINGE', 'REDBAN', 'ABERDEEN', 'THE COS OF ZEALAND', 'RIE'.
'N N E S S W', 'GRAVESEND', 'SANDWICH', 'WEST END OF WIGHT', 'THE MAAS', 'WEILING', 'BLACKES'.
'N E B N S W B S', 'DVNDE', 'SAINT ANDREWS', 'LISBOANE', 'S MATHEWS' 'FOT EVAN', 'S LVCAS', 'CAALS'.
'N E B E S W B W', 'THE COS OF BISC', 'GALICA PORTV AND SPAINE', 'SILLE ILES', 'BROVAGE', 'BVRDIS', 'ROANE'.
'E N E W S W', RITH LEETH', CARBVROW', 'THE COST OF IRELAND', 'SEVERN', 'HOLAND', 'DVNBAR'.
'E B N W B S', 'FALMOUTH', 'THE ILE OF IARNSEI', 'TORBAIE', 'CADLE'.
'E B S W B N', 'HARTELPOOL', 'BRISTOW'.
'E S E W N W', 'BRIDGWATER', 'MILFVRD HA', 'START POIN', 'AT THE LISSERT', 'TEXEL', 'FOIE'.
'S E B E N W B W', 'PEERPORT', 'PORTLA<N>D'.
A quartered square in the centre is inscribed as follows:
'EW moone', 'ANTWERP', 'HV<M>BERLIN', 'DART<M>OUTH', 'PLIMOUTH'.
'NS moone', 'QVINBOROW', 'SHAMTVN' 'PORTSMVTH', 'FLA<N>DE COS', 'DOVER'.
'NE SW', 'LONDON', 'TINMOVTH', 'HARELPOOL', 'NANTS RIV', 'YARMOVTH'.
'NW SE', 'POOLE', 'ORWELL', 'ALL THE COS OF FRISLAND'.
The inside of the bottom cover is laid out as a perpetual calendar and an Easter table, inscribed in the centre 'This Tabell Begineth at 1593 and so for euer.'
The three outer circles give the dates of saints' days, Christian feasts and the entry of the sun into a particular sign as follows: 'I 1 Circum', '6 Epiphani', '11 [Sun] [Aquarius]', '25 Con paul'; 'F 2 purifi', '9 [Sun] [Gemini]', '14 Valentin ', '24 mathi'; 'M 11 Sun in [Aries]', '25 Anunsiatio' 'A 11 [Sun] [Taurus]', '23 George', '25 Marck euange'; 'M 1 Philip and Iacob', '12 sun in [Gemini]'; 'I 11 bar<n> a' , '12 [Sun] in [Cancer]', '24 Io bap', '29 pet pa'; 'I 6 dog be', '13 [Sun] [Leo]', '22 Mari Mag', '25 Iames ap'; 'A 14 [Sun] [Virgo]', '17 dog e<n>d', '24 barth', '29 Ion be'; 'S 14 [Sun] [Libra]', '21 Matew', '29 micaell'; 'O 14 [Sun] [Virgo]', '18 Luck euan', '28 Simon and Iud'; 'N 1 all saints', '13 [Sun] [Sagittarius]', '30 Andrew apo'; 'D 12 [Sun] [Capricorn]', '21 tho<m>', '25 natiui', '26 ste'.
Five circles in the centre are marked with the Easter dates ('Easter da'), the Golden numbers ('Prime'), the 'Epact'(s), and the Dominical letters for common ('dominic') and leap ('leape') years. The Easter dates in March are marked with a 'm', those in April with an 'a'.
The outside of the bottom cover is inscribed with different scales as follows (from the outside:
1) A zodiacal scale, marked with the Latin names of the zodiacal signs and their symbols. Each sign has a 30? scale, numbered by 10 and divided to 2.
2) A calendrical scale with the English names of the months ('Ianneuari, Februari, March, Aprill, Maie, Iune, Iulie, August, September, October, November, December') and the corresponding number of days, numbered by 10 and divided to 2.
3) A scale with 32 compass points, indicated by their first letters.
4) An hour scale marked twice I to XII. Further to the inside are two volvelles of decreasing size, both with an index. The larger one has a scale of the age of the moon 1 to 291/2, numbered by 1. The smaller one has the signature and the date 'Iames Kynuyn fecit 1593' and part of an planetary aspectarium. A circular aperture shows the phases of the moon.
The instrument was presented by Edward Dalton in 1866 and is described in J. Bruce, "Description of a Pocket Dial Made in 1593 for Robert Devereux, Earl of Essex'", Archaeologia 40 (1866), pp. 343-56; 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. 126, no. 361.