Iranians use three calendars in daily life:

- Gregorian calendar for practical matters

- Islamic calendar for religious matters

- Persian calendar for matters of hubris

The modern Persian calendar is a solar calendar (sharing the same year 0 as the Islamic calendar), and the first day of the year is always synchronized with the Spring equinox.

Edit: Although the Persian and Islamic calendars share the same initial year, the (lunar) Islamic calendar is 11 days shorter. Over time, this has resulted in the current year being "decades" apart between the two.

https://en.wikipedia.org/wiki/Iranian_calendars#Modern_calen...

Japan also uses the Gregorian Calendar. I think the Emperor era designation is an informal thing, as in daily life it would be to complicated.

The Imperial era years are quick commonly used on official forms. If you live in Japan you will soon learn the current year and the year you were born. The Gregorian Calendar years are also common, and the New Year is on the same day.

Japan's date system is unusually complicated in that it has such a long history of being continually reset: http://www.sljfaq.org/afaq/era-list.html

yes exactly.the lunar calendar is 10 days shorter! and it's rotating. the Arabs previous to Islam had a calendar that was more accurate, then Islam just removed 10 days from it and it is rotating now !