Christmas falls 13 days later on that calendar than it does on the Gregorian calendar used by most church and secular groups.

Source: https://www.barryanddistrictnews.co.uk/news/national/23688557.ukraine-moves-official-christmas-day-holiday-shift-russian-tradition/?ref=rss

Demon haunted and god haunted, he emerges from the company of Odin and Thor into the High Middle Ages – the world of illuminated manuscripts, Romanesque sculpture and Gregorian chant.

Source: https://www.thecourier.co.uk/fp/entertainment/culture/3997921/pillagers-of-scotlands-east-coast-how-the-greatest-viking-legacy-of-late-author-desmond-seward-lives-on/

He said, based on the Gregorian calendar three (3) months makes one quarter and there are 12 months, making four quarters in a year.

Source: https://newsdiaryonline.com/pdp-chieftain-drags-ag-chairman-others-to-court-over-alleged-negligence-of-party-constitution/