Kirigocha is a semi-automatic machine for distance measurement.
According to “Sejongsillok” (Chronicles of King Sejong), kirigocha was first used in March, 1441, which means that it was used for measuring distances in Korea in the mid-fifteenth century.
No records at the time of building it have been found. Instead, its structure is described in the book “Juhaesuyong” written by Hong Tae Yong (1731~1783), a realist and materialist of the eighteenth century.
According to it, two cogwheels that are placed one upon another in the box on a cart engage tightly with the vertical cogwheel attached to the wheels. The rotations of the wheels make the sounds of a bell and a drum, which indicate distances.
In other words, the rolling of the wheels over a half ri (1ri=392.73m) and one ri rings a bell once and several times, respectively, while the drumbeat is heard once after 5 ri and several times after ten ri. The distance is measured in ri according to the sounds of the bell and the drum.
Distance measurement by kirigocha was more accurate than that by a tape measure.
The distance of longitude 1° measured 108 kilometers by kirigocha, which means the measurement error limit is below 3%, compared with the current value 110.95 kilometers. This proves that kirigocha was perfect for measuring distances.
To sum up, kirigocha demonstrates Korean ancestors’ high mathematical talent and creative wisdom.
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