Two sundials are engraved side-by-side on a single stone tablet. The “ganpyeong-ilgu” (簡平日晷, Simplified Plain Sundial) at the top features a circle with a mark indicating the North Pole and the “hongae-ilgu” (渾蓋日晷, Sundial of Concealed Heaven) at the bottom features a circle surrounding the South Pole. The ganpyeong-ilgu is a circle divided by vertical hour-lines and horizontal declination lines indicating the 24 seasonal subdivisions. The hongae-ilgu is a circle divided by a set of radiating arcs indicating the hours and a straight vertical line towards the south which denote noon.

The inscriptions at the bottom reads as following:

“Hanyang, 37 degrees 39 minutes and 15 seconds, north latitude”
(漢陽北極出地三十七度三十九分一十五秒) “Maximum distance between the Ecliptic and the Equator by the Shixian Calendar, 23 degrees and 29 minutes”
(時憲黃赤大距二十三度二十九分) “Constructed on the mid-autumn day, the Year of Eulsa, 50th year of the reign of Qianlong ”
(乾隆五十年乙巳仲秋立)

The first line of the inscription tells that these sundials were produced in the standard of the north latitude of Hanyang, today’s Seoul. The latitude of 37° 39' 15" was measured at Jongno in 1713 (39th year of King Sukjong’s reign). The second line indicates the maximum distance between the Ecliptic and the Equator measured 23° 29', based on the Shixian Calendar of the Qing dynasty. The third line signifies the production date, the 15th day of the 8th lunar month, 1785 (5th year of King Jeongjo’s reign).

Rubbing of the two sundials