Ottoman perpetual calendars were not official calendars that astrologers had to prepare as part of their duties, unlike annual calendars. These calendars encompassed a wide range of authors, including mystics and bureaucrats. Therefore, they could vary in content and visual presentation, bearing the imprint of their creators. Among the most intriguing examples are the volvelles occasionally found within perpetual calendars. An example of an Ottoman volvelle from the seventeenth century, kepts in the Rare Books and Manuscripts Library at Columbia University, consists of five concentric circles. The outer circle is divided into twelve sections representing the zodiac signs. Moving upwards from the bottom, the movable parts are as follows: a plate containing the names of the Hijri months, a plate representing the days of the week in Arabic alphanumeric notation, a plate depicting the remaining numbers after dividing the Hijri year into eight parts, a plate representing the disk of the Sun, and finally, a plate representing the movement of the Moon as the last component of the volvelle.
For the source of the image, see Calendar for year 1064 AH, New York, Columbia University, Rare Book and Manuscript Library (Nadir Eserler ve El Yazmaları Kütüphanesi), MS Or 24, 8b.
For detailed information, see:
Danışan, G. (2021). The Paper Instruments in the History of Ottoman Astronomy. Bulletin of the Scientific Instrument Society, No. 149: 37. https://www.academia.edu/49139870/The_Paper_instruments_in_the_History_of_Ottoman_astronomy