The Chinese calendar which was used by the Qing Dynasty, used a method for determination of 24 divisions of the old calendar based on the ecliptic cycle, in which an interval between 24 divisions of the old calendar varied, and in the Kakei era (China) rules were revised to call the month including the Spring equinox February (Kisaragi).
清代で採用した時憲暦では二十四節気の間隔が変動する定気法を採用したため、嘉慶(中国)年間より春分を含む月を2月（如月）と呼ぶように規則が変更された。