The Gihō-reki system was brought from Korea to Japan in Yi-feng era (676-678) of the reign of Emperor Gaozong of Tang. This calendar corrected errors in the Yuan-jia li (Genka calendar) which was developed in China. For a short time, both Genka and Gihō calendars were in use.
- Nussbaum, Louis-Frédéric. (2005). "Calendar" in Japan Encyclopedia, pp. 98-99; Bramsen, William. (1880). Japanese chronological tables, p. 25.
- Clement, Ernest W. (1902). "Japanese Calendars," in Transactions of the Asiatic Society of Japan, Vol. 30-31, pp. 1-82, 72.
- Pak, Song-nae. (2005). Science and technology in Korean history, p. 46.
- Japan, Monbushō. (1876). An outline history of Japanese education: prepared for the Philadelphia International Exhibition, 1876, p. 160.
- Charlotte von Verschuer (1985). Les relations officielles du Japon avec la Chine aux VIIIe et IXe siècles (Hachi-kyū-seiki no Nitchū kankei), pp. 243-245 n. 114. (French)