The Cham calendar (Cham language: sakawi) is a lunar calendar used by the Cham people of Vietnam since ancient times.
System
The names of the days of the Cham week were derived from their Sanskrit names used in the traditional Hindu calendar.
The length of the month: the full month has 30 days (Cham language: balan tapăk) and the hollow month has 29 days (Cham language: balan u).
References
Cham calendar Wikipedia(Text) CC BY-SA