The Yerm Lunar Calendar is a simple pure lunar calendar invented by Karl Palmen in 1998. The months are grouped into yerms, so that every odd-numbered month of the yerm has 30 nights and every even-numbered month of the yerm has 29 nights without exception. Having a 3-yerm cycle where two yerms have 17 months and one yerm has 15 months would produce a fairly accurate mean month of 29.530612 days. This is called the Basic Yerm Calendar. This 3-yerm cycle has 49 months and is exactly 14 days short of four years including one leap day.