Strabo states that he discovered that the solar year is longer than 365 days by 6 hours; Vitruvius that he invented a sun-dial.
You will use either the solar year or the year prior.
Everyone else can use the solar year to look up your favored element.
Both festivals, of course, belong to a lunar calendar, and move through the solar year every thirty-two years.
The civil year consisted in general of twelve months or lunations, but occasionally a thirteenth was added in order to preserve its correspondence with the solar year.
