This is a perpetual calendar based on the 19 year “Metonic” cycle of the moon which does not rely on knowledge of the length of the tropical year or the occurrence of leap years. It is simply set at the beginning of each year by marking the first full moon after the winter solstice. It can still be used today.
Notably, the first full moon marks the date of Disting, an important Celtic feast and fete day which everyone could remember. Apart from the central calendar wheel, which groups the days into a typical month, the tablet records a double line inscription running down both sides.
On the first line, 52 weeks of seven days are laid out using 52 repetitions of sixteen runes of Younger Futhark, plus special symbols adopted for the remaining three years, Arlaug, Tvimadur and Belgthor.
On the second line, many of the days are marked with one of the symbols which relate to the 19 years of the lunar cycle. The runes for each weekday vary from year to year and the new moon always falls on the given day during that year of the cycle.
http://www.archaeologyhub.info/ancient-viking-rune-stone-lunar-calendar/#.VsfBqC04bDk.facebook
