There have been at least four similar reforms of the lunisolar version of the Hindu calendar, all intended to make the month a better match to the lunation and to make the year a better fit to the "sidereal" year. There have been reforms of the "solar" version of the Hindu calendar which changed the distribution of the days in each month to better match the length of time that the Sun spends in each "sidereal" zodiacal sign. The same applies to the Buddhist calendar. The first millennium reform of the Hebrew calendar changed it from an observational calendar into a calculated calendar. The Islamic calendar was a reform of the preceding lunisolar calendar which completely divorced it from the solar year.