Equatories. Planetary Equatorium. Astronomical Instruments‪.‬

The text of a Persian manuscript in the Garrett Collection at Princeton University. The manuscript describes the construction and use of two astronomical computing instruments.
The instrument called by Kashi Tabao al-Manatiq, which we translate as "Plate (or Tray) of Heavens." It is an example of the class of devices known as equatoria, analogue computers on which the various Ptolemaic planetary configurations were laid out to scale. They thus yield solutions to such problems as that of finding the true longitude of a planet at a given time.
The second instrument, the "Plate of Conjunctions" (Lawh al-Ittlsalat), is a simple device for performing a linear interpolation.