Another theory holds that the Koyomi (almanac/calendar) which derives from Tsukuyomi (moon-reading), originally a method to calculate the number of days since the new moon, was used to count the number of days until the new year--when the spirits of one's ancestors return from Yomi as Toshigami (gods that dwell in one's house during the new year holiday).
また、元来月齢算出をあらわす月読(ツクヨミ)から派生した暦（こよみ：黄詠み）は、祖霊(おやがみ)が常世(黄泉)から歳神(としがみ)として還ってくる正月を算出するための日数演算法という説もある。