Therefore, some form of addition to the lunar year (of intercalation) is necessary.The overall basis for it is provided by cycles of 57 years.In Burmese Buddhist tradition, it was 13 May 544 BCE (Tuesday, Full moon of Kason 148 Anjanasakaraj).

In Sri Lanka, the difference between BE and CE is 544.

But the solar month varies by the type of year such as tropical year, sidereal year, etc.) The days of the month are counted in two halves, waxing and waning. The civil new moon day is the last day of the month (14th or 15th waning).

One of its primary objectives is to synchronize the lunar part with the solar part.

The lunar months, normally twelve of them, consist alternately of 29 days and 30 days, such that a normal lunar year will contain 354 days, as opposed to the solar year of ~365.25 days.

Because of the inaccuracy of the calendrical calculation systems, the mean and real (true) New Moons rarely coincide.

The mean New Moon often precedes the real New Moon.

One major difference is that the Southeast Asian systems, unlike their Indian cousins, do not use apparent reckoning to stay in sync with the sidereal year.

Instead, they employ their versions of the Metonic cycle.

The intercalary month not only corrects the length of the year but also corrects the accumulating error of the month to extent of half a day.