This calendar is an inexpensive way to get your ad noticed all year long without breaking the bank. The same ad message prints on both sides of the tent mount. Trivia:The Jewish calendar is based on the Metonic cycle of 19 years, of which 12 are common (non-leap) years of 12 months and 7 are leap years of 13 months. To determine whether a Jewish year is a leap year, one must find its position in the 19-year Metonic cycle.