Epact Scientific Instruments of Medieval and Renaissance Europe

The back has an outermost degree scale 90 to 0 to 90 to 0 to 90, divided to 5, subdivided to 1, numbered by 10. Within this is a zodiacal scale, with the names and symbols of the signs, each having a 30-degree scale divided as the degree scale. Next is a scale of the 28 lunar mansions, containing 12 or 13 days, then an eccentric calendar scale, with the Latin names of the months, each with a scale of days, divided to 5, subdivided to 1, numbered by 10 as appropriate. The central space has a double shadow square with scales 0 to 12 to 0 to 12 to 0, divided to 3, subdivided to 1, numbered by 3, and a diagram for unequal hours. Dated '1490' and signed 'h b' with Hans Bamman's triangular mark.