The Gregorian dates on the Ogam Wheel are approximate. This is because the tree calendar has its own leap days on different days to the Gregorian calendar. The leap day rule of the tree calendar is not known. However, any leap day rule will work for the Ogam wheel provided that it ensures that the solstices occur on or very close to their allotted tree calendar dates (of Oak 12 and Elder 27).
Exactly one of the following actions must be taken when moving the Ogam wheel over a leap day,
The 19-year cycle is accurate only for a few hundred years. It can be corrected by skipping 8 golden numbers in the 19-year cycle about once ever 3 or 4 hundred years. The Ogam wheel will also work for tree calendar dates based on the Julian calendar, but the 19-year cycle needs to be corrected differently and so a different golden number would normally apply to each year.
Karl Palmen 8 December 2005