Sejong ordered royal officials to develop a calendrical method that would facilitate accurate calculation. The following 12 years of labor and research came to fruition in a work entitled ~. It was a landmark in the history of astronomical science, including details of the movements of the sun and moon, as well as Mars, Mercury, Jupiter, Venus and Saturn. It fully incorporated the calendrical theories of China and Arabia, adjusting them with reference to the latitude of Seoul. As a result, Choson astronomers were able to calculate the position of all the planets with respect to the Korean capital, as well as the times of sunrise and sunset, and solar and lunar eclipses. The book calculates one year to be~, values correct to six significant figures according to modern calculations. The work is regarded as one of the most remarkable astronomical achievements of its day. The work was introduced to Japan by an envoy named ~ in the 17th century, and Japan later published its own astronomical calendar. When the book was completed in 1442, however, only ~ were able to compute(calculate) celstial(astronomical)~ to such a high degree of accuracy, and with respect to (with reference to)~.