The Reki Hakase belonged to the Bureau of Onmyo in the Nakatsukasa Department, and was responsible for the preparation and revision of the annual calendar, forecasting solar eclipses and educating Reki no sho (students of calendar preparation).
中務省陰陽寮に属して、毎年の造暦（暦の作成）と改暦、日食の予測、暦生の教育にあたった。