Islamic chronology dates back to Hijra (16th July, 622CE), the date of the resettlement of the Prophet Muhammed and the first Muslims from Mecca to Medina, which is why in Islamic countries the calendar is called the “Hijra” calendar. For that reason, Konstantin Chaykin gave his wristwatch with an Islamic calendar indication the name “Hijra”.
A peculiarity of the traditional Islamic lunar calendar is that it is both simple and complex. Its simplicity in following the lunar cycle is at first straightforward, with a rather rough approximation of a repeating 29.5-day period. Then the difficulties begin – in order to coordinate the calendar with the actual length of the lunar month of 29.53059 days, various leap-year cycles are introduced to the Islamic calendar, usually using the 30-year Arabic cycle with 19 regular years of 354 days and 11 leap years of 355 days. Alternatively, the 8-year Turkish cycle is used, with 3 leap years in which an extra day is added to the last month of the leap year.
Konstantin Chaykin took all the specific features of the Islamic lunar calendar into account in his patented movement, displaying the phases of the moon, and also the date, month and day of the week of the Islamic calendar. Chaykin’s Islamic calendar system works as an annual one, that is, its manual correction in alternating 29- and 30-day months is required no more than once every two years, namely in the leap years of the Islamic leap year cycle, whether following the 30-year Arabic cycle or the 8-year Turkish cycle.
The straightforward mechanics of Chaykin’s Islamic lunar calendar system impressively show themselves in cases of discrepancies in determining the beginning of the month – in this case, the watch owner has everything necessary for a quick, convenient calendar correction should it be needed. The start of the month can shift according to an astronomical sequence of events (which can be by one, two or even three days), therefore, in order to give the watch owner full confidence in following the chosen calendar tradition, Chaykin equipped the watch with a day of the week indication. Indeed, as the weekly cycle is continuous you can always rely on it.