A calendar which had its new year's day on its Easter that fell on a Saturday (or a holy Friday), was used in France in the 11th to the 16th Centuries, and Easter is a movable holiday and its same date comes every two years.
イースターの土曜日（又は聖金曜日）を正月とする暦は、フランスで11世紀～16世紀に使われていた　イースターは移動祝日で、同じ日付は隔年ごとに来る。