Half of the rete consists of a "folded" star map up to the equator, with the northern and southern hemispheres superimposed. Such a combined north-south instrument is called an equinoctial astrolabe (Maelcote astrolabe, described around 1600 by the Jesuit van Maelcote in Brussels). The other half of the reed forms a perforated azarchel grid (stereographic projection of the celestial sphere) and, together with the azarchel insert disc, serves to convert spherical coordinates.
The original inlay plates contain double "folded" 3° almucantarats (altitude circles above the horizon), whose application is hardly manageable. In addition to a sample plate for 6°, 12°, 18° and 24° latitude, this replica contains two plates with half-almucantarats for 24°, 30°, 36°, 42°, 48°, 54°, 60° and 66° latitude. All are also engraved below the horizon for use as a north or south astrolabe.
To make it easier to use, the replica contains an additional Latin equinoctial rete without an azarchel grid and, therefore, not folded. It contains the same 18 stars as the Arabic rete and four additional stars. There is a zodiac and calendar division on the Latin rete (0° Aries = March 11).
The reverse shows a special azarchel construction in the upper half (determining the directions of prayer?) and the juxtaposition of the ecliptic and Syrian calendar at the bottom.
A double shadow square with the divisions 7 and 12, as well as signature and date, complete the "record" astrolabe of Ibn al-Sarraj.
The complete description of the instrument as PDF for download
