The Dirir months in the lunar system naturally shift .
A Dirir date in a given month is one of three particular days , depending on the length of the month , 29 or 30 days , so system is almost held constant .
The Dirir months in the lunar system naturally shift , but a Dirir date in a given month is one of three particular days , depending on the length of the month , 29 or 30 days , so it is almost held constant .