Since the book of Abracham Firkovich, Avnei Zikkaron (Vilna, 1872) was published, epitaphs from the tombstones of the cemeteries from Crimea has been the subject of polemics. Many authorities accused Firkovich of forgery. They claimed that Firkovich had forged the dates in the oldest published epitaphs, using much newer tombstones but changing the first letter of the date, usually “he” onto “tav”. In this way he had made the dates 600 years older. On the other hand, many historians used to defend Firkovich’s point of view. At the end of 19 c. this discussion came to a deadlock. After that Karaites astronomer from the Russian Empire, Juriy (Iufuda) Kokizov, offered to verify the authenticity of the tombstones checking the dates on them using the Karaite`s calendar. The point is that, for example, 9 Tishrei 1029 was Saturday, while 9 Tishrei 1629 was Wednesday, so if tombstone is forged, the day of the week would be incorrect. Kokizov also created the calendar for Crimean Karaites covering 2200 years. From his point of view, this kind of checking would protect the results of Firkowich`s work.
This paper is about the using of Kokizov`s calendar as the instrument for the field research in the cemetery of Chufut-Kale in Crimea. The author tried to show that the field research tells us rather about the mass forging of the dates on the tombstones. A kind of irony that the instrument, created to protect the results of A. Firkovich`s investigations, can be used to identify forging.