When the year of Emperor Jimmu's enthronment "the year of kanototori" is calculated on the basis of the period of reign of successive emperors, it falls on 660 B.C., and the month of his enthronment was "harushogatsu," which is around the first day of spring, and the date of the enthronment (eto) was "Kanoetatsu."
神武天皇の即位年の「辛酉年」は『日本書紀』の歴代天皇在位年数を元に計算すると西暦紀元前660年に相当し、即位月は「春正月」であることから立春の前後であり、即位日の干支は「庚辰」である。