Epact Scientific Instruments of Medieval and Renaissance Europe

On the other side of the plate is a quadrant of degrees divided from [0?] to 90? by 1? and numbered by 10?, a zodiac scale divided to five and to one degree, numbered by ten from [0?] to 30?, with the symbols of the zodiacal signs. Further to the centre is a zodiac and calendar scale divided to the single day, with the symbols of the zodiacal signs numbered from 1 to 12, the names of the months and the 10th, 20th and last day numbered. Further to the centre is a table of epacts with prime and dominical letters. In the centre is the inscription 'S letter G Prime 17 Epact [star] 1593'. At the lower edge of this side is a further scale numbered each way up to 12 over an arc of 60?. The alidade, with folding sight-vanes, is engraved with arabesques and the screw appears to be a later replacement. The top and bottom parts of the dial side are also decorated with arabesques and foliage.

Soma scholars have raised doubts about the authenticity of the instrument, citing as evidence some of the constructional details of the instrument; the acanthus leaf pattern on the alidades, the folding gnomons, and the 30 Whitworth/90 metric thread on the central bolt which screws into an original tapping. The engraved lettering is fairly similar to Whitwell's script as known from other instruments signed by him, but according to these scholars, the intrusive 'h' in Whitwell's first name is suspicious, as he normally signs 'Carolus'.