Lunar calendars suffer from an inherent uncertainty in the length of each month and the number of months in the year. Variable atmospheric conditions, weather and the acuity of the eye of an observer mean that the first sighting of the new moon crescent can never be known in advance. Calendars which rely on such observations to define the beginning of a new month therefore suffer from this lack of certainty as to whether a month will begin on a given day or the next. The papers in this volume ad