This dial is made in the form of a book, with hinged front and back covers. The outer parts are extensively engraved with religious inscriptions. The outer part of the upper leaf has a shield at the top, with the initials 'IHS', and is inscribed 'FGVRA PRI<N>CIPIOR I<N>STRVME<N>TI SCIENDI'. Below is a series of six concentric circles, inscribed respectively: in the first circle, 'B. BONITAS', 'C. MAGNITV', 'D. DVRATIO', 'E. POTESTAS', 'F. SAPIENTIA', 'G. VOLVNTAS', 'H.VIRTVS', 'I. VERITAS', 'K.GLORIA'. The second circle is inscribed 'D<IFFE>R<ENTI>A', 'CONCORDANT<IA>', 'CONTRARIETAS', 'PRINCIPIVM', 'MEDIVM', 'FINIS', 'MAIORITAS', 'AEQVALITAS', 'MINORITAS'. The third circle is inscribed 'VTRVM', 'QVID', 'DEQVO', 'QVARE', 'QVANTVM', 'QVALE', QVANDO', 'VBI', QVO & EAQVO'. The fourth circle is inscribed 'DEVS', 'ANGELVS', 'CELVM', 'HOMO', 'IMAGIN<IS>', 'SE<N>SITIVA', 'VEGETAT<IO>', 'ELEME<N>TA', 'INSTRVME<NTA>'. The fifth circle is inscribed 'IVSTITIA', 'PRVDENT<IA>', 'FORTITV<DO>', 'TEMPER<ANTIA>', 'FIDES', 'SPES', 'CHARIT<ATIS>', 'PATIE<N>TI<A>', 'PIETAS'. The sixth circle is inscribed 'AVARIT<IA>', 'GVLA', 'LVXVRI<A>', 'SVPER{BIA}', 'ACIDIA', 'INVIDI{A}', 'IRA', 'ME<N>DAT<IO>', 'INCO<N>ST{ANTIA}'. At the centre of the circle are the corresponding letters of the alphabet from 'B' to 'K', and at the very centre, 'CHAOS'. In the corners is the inscription 'BONITAS DEI AT ORIGO MVNFACTIO OMNIVM RERVM'. At the bottom of the leaf, close to the hinge, is 'AL' and 'RI', and at the centre, 'BONITATEM DISCIPLINA<M> ET SCI<ENTI>AM DOCE ME. PSAL.'. Two catches keep the leaf closed when not in use.

The inner side of the leaf has on the top left corner the letters 'A', 'B', 'C', in a divided square. On the right hand side are two circles with their centres named 'A' and 'B', on two opposite edges of another square. In the centre of the band on the top of the leaf is the inscription 'SAPIENTIA AEDIFICAVIT SIBI DOMVM. Prouer. 9' and 'MAGNA ET MIRABILIA SV<N>T OPERA TVA D<OMI>NE. APOC. 15'. In the centre of the leaf is a five-pointed star, centred on 'sensus communis', where the rays are 'VISVS', 'AVDITVS', 'ODORAT<VS>', 'GVSTVS', 'TACTVS'. Three rings encircle the star, and are engraved, from the centre, anticlockwise with 'DVBITABILE', 'IMAGINABILE', 'SENSIBILE', 'INTELLIGIBILE', 'CREDIBILE' on the first ring. On the second ring are anticlockwise 'NATVRA', 'SVBL<IM>A', 'ACC<IDE>NS', 'SI<M>PLEX', 'CO<M>POSIT<O>', 'INDIVI<DVALIS>', 'SPE<CIE>S', 'GENVS', 'ENS', 'ACTVS', 'PASSIO', 'ACTIO'. The third and last ring is engraved clockwise with 'ANGELVS', 'COELVM', 'HOMO', 'BRVTVM', 'PLANTA', 'FLAMMA', 'LAPIS', 'DEVS'. In the corners of the square enclosing the rings is the inscription 'INVISIBILIA DEI A CREATVRA MV<N>DI PER EA QVE INTELLECTA FACTA SVNT CO<N>SPICIVNTVR'. In the top left corner are four circles, concentric two by two, with the letters 'E', 'V', 'B', 'V'. In the top right corner is a tripartite circle with the letters 'T', 'R', 'C'. On the right and left hand sides of the main figure are engraved the words 'SCALAE' 'INTELLECTVS'. At the bottom is another band, engraved with at the centre, three concentric squares and a circle, engraved 'QVADRATVRA CIRCVLI'. At the far left are four circular sectors with two perpendicular external tangents, and at the far right a table with the combinations of the letters A, B, C, D. Between the geometrical figures is the inscription 'NISI CREDIDERITIs NO<N> INTELLIGETIS'.

Inside the box is a gilt brass plate with a compass in the centre with two armillae, with a weight inside so that it remains horizontal. The compass is marked for magnetic deviation and with the initial of the cardinal points 'T', '[cross]', 'O', 'P'. One side of the plate has the names of the cardinal points and winds in Italian engraved on the borders, 'TRAMONTANA', 'Greco', 'LEVANTE', 'Scirocco', 'OSTRO', 'Garbino', 'PONENTE', 'Maestro'. Intertwined between the letters are symbols resembling the sun, two concentric circles with rays. The top of the plate has a pin gnomon dial for 'Polus 45 Graduu<m>' indicating Italian hours with continuous line from 9 to 23, and common hour lines with punctuated lines from five to twelve to seven, numbered by one from VI to XII to VII.

The bottom part of the plate has a pin gnomon dial for 'Latitudo 42 Graduu<m>', indicating Italian hours with continuous lines from ten to 23, numbered from 11 to 23, and common hours with punctuated lines from five to twelve to seven, numbered from VI to XII to VI.

The mid-line of the plate is inscribed 'Horae {ab} Occasu cu<m> As{tronomicis} Punctuatis'. Part of the inscription is covered by the compass hinges.

The other side of the plate is similarly engraved with the winds and cardinal points 'SEPTENTRIO', 'Boreas', 'SOLANVS', 'Eurus', 'MERIDIES', 'Aphricus', 'FAVONIVS', 'Circius' and with sun effigies as in the other side. On the top part is a pin gnomon dial 'Ad polu<m> 45 Graduu<m>', indicating Babylonian hours with continuous lines from 1 to 15, and unequal hours with punctuated lines from I to II [eleven].

The bottom part of the plate has a pin gnomon dial 'Ad latitudine<m> 42 Graduu<m>' indicating Babylonian hours with continuous lines from 1 to 15, numbered to 14, and unequal hours with punctuated lines from I to II [eleven].

The inner part of the back of the box is inscribed 'FIGURA DEMONSTRATIVAE' on the top. At the centre of the leaf is a circle, centred on a triangle inscribed 'T'. Inside the first circle is the inscription 'BENEDICTA SIT SANCTA TRINITAS ?'. In the circle are six engraved rings, starting from the centre, with 'TERRA' 'AQVA', 'AER', 'IGNIS' on the first and the second. The third and fourth circles are inscribed 'A','Z', 'Y', 'X', 'V', 'T','S'. The last two circles are 'B' to 'R' in the Latin alphabet. In the four corners are the inscriptions 'GLORIFICATE DEVM IN DOCTRINIS', and on the bottom 'QVAECVNQ<VE> SCRIPTA SVNT AD NOSTRAM DOCTRINAM SVNT SCRIPTA' and a simple foliage.

The outer part of the leaf is engraved with five concentric rings, centred on Christ's monogram, and three swords. In the first ring is 'SANCTVM ET TERRIBILE NOMEN EIVS [three dots]'. The second ring is engraved with 'BENEDICTVM AMEN SIT NOMEN DOMINI'. The third ring has 'CAPITALIA PECATA ALIENA IN SPIRITV S<AN>CTVM IN COELV<M> CLAMA<N>TIA'. The fourth ring is inscribed 'VIRT. CARD. DONA & fructus sp<irit>us s<an>cti BEATITVD. COSILIA NOVISSIMA IVSTITIA TRIA Gu[?]ra bonorum operum'. The fifth and last circle is inscribed 'SACRAMENTA SAPIENTIA FIDES SYMBOLVM SPES AVE M<ARI>A PATERN<OSTE>R CHARITAS P<IE>TA DECAL. ET ECC'. In the four corners are inscribed the words 'INITIVM SAPI<ENTI>AE TIMOR DOMINI', and at the bottom, 'ANTE OBITVM OPERARE IVSTITIAM Q<VORV>M NO<BIS> EST APVD INEBROS INVENIRE CIBV<M> ECCL. 14.'

The sides of the box are inscribed 'LVCERNA INSTRVMENTALIS', 'INTELLECTVS DIRECTIVA', 'SIVE INSTRVMENTV<M> SCIENDI.'

On the inner side of the box, near the hinge, is the signature 'Carolus Platus F. Romae A<nn>o 1593'.

The instrument was purchased in 1922 and is described in 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. 44, no.109.