In a brass frame with horizon ring (engraved with 16 old wind names: Tramontana = north, Mezzodi = south, Levante = east, Ponente = west, etc.), the meridian circle is located vertically, supporting the celestial sphere that rotates around the pole axis. This consists of the four columbar arcs, the ecliptic ring and the tropics and polar circles. In its entirety, this instrument illustrates an armillary sphere.
The meridian circle can be moved in the frame and allows the geographic latitude to be set from 0°-90°. At the same time, the edge of the meridian opposite the latitude scale serves as an index for reading the hours. This index edge has a correction scale; it is necessary because the time reading is in the ecliptic and must therefore be converted to true equatorial time.
In order to obtain the mean local time, the equation of time must be taken into account as a further correction. We find the values of this equation of time on the fixed ecliptic ring, which has three scale circles: the Gregorian date circle (vernal equinox = March 21) and two number circles on the inside with the values of the equation of time in minutes, whereby the lower circle (with the month names) contains negative values (e.g. mid-November: - 16 min.) and the upper, innermost circle, the positive values (e.g. beginning of January: + 6 min.).
The ecliptic consists of the aforementioned fixed date ring and the hour ring with the two graduation plates that can be moved on it. Two shifted sun rays are necessary to avoid possible occultations by meridian, colur rings etc. There is an arrow on the sighting plate with the holes that is to be set to the date. The hour scale in the plane of the ecliptic leads to deviations from the correct position of the hours in the equatorial plane. The corrections required to determine the true local time are indicated on the meridian ring.
The complete description of the instrument as PDF for download
