The Yang-gyeong-gyu-il-ui (兩景揆日儀) is a kind of elevation sundial using three wooden plates. Sang-hyeok Lee (李尙爀, 1810~?) and Byeong-cheol Nam (南秉哲, 1817~1863) gave descriptions of this sundial and explained how to use it in their Gyu-il-go (揆日考) and Ui-gi-jip-seol (儀器輯說), respectively. According to Gyu-il-go (揆日考) there are two horizontal plates and two vertical plates that have lines of season and time. Subseasonal (節候) lines are engraved between seasonal (節氣) lines, subdividing the interval into three equal lines of Cho-hu (初候, early subseason), Jung-hu (中候, mid subseason) and Mal-hu (末候, late subseason); there are 13 seasonal lines for a year, thus resulting in 37 subseasonal lines; also, there are 12 double-hour (時辰) lines for a day engraved on these plates. The only remaining artifact of Yang-gyeong-gyu-il-ui was made in 1849 (the 15th year of Heon-jong) and is kept at the Korea University Museum. We have compared and analyzed Yanggyeong- gyu-il-ui and similar western sundials. Also, we have reviewed the scientific aspect of this artifact and built a replica. Yang-gyeong-gyu-il-ui is a new model enhanced from the miniaturization development in the early Joseon Dynasty and can be applied to the southern part of the tropic line through a structure change.

1. INTRODUCTION
 2. ELEVATION DIAL
  2.1. Shepherd's Sundial and Elevation dial of the West
  2.2. Hour and Seasonal Lines of Yang-gyeong-gyu-il-ui
 3. SHADOW OF THE HORIZONTAL AND THEVERTICAL
 4. THE STRUCTURE OF THE HOENG-PYO-IP-PYOIL-GU
 5. CONCLUSIONS
 ACKNOWLEDGEMENTS
 REFERENCES

• Yong Sam Lee(Department of Astronomy and Space Science, Chungbuk National University, Cheongju 361-763, Korea)
• Sang Hyuk Kim(Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea, Korea University of Science & Technology, Daejeon 305-350, Korea) Corresponding author
• Byeong-Hee Mihn(Department of Astronomy and Space Science, Chungbuk National University, Cheongju 361-763, Korea, Korea Astronomy and Space Science Institute, Daejeon 305-348, Korea, Korea University of Science & Technology, Daejeon 305-350, Korea)