Jeong Yak-Yong invented Geojunggi, which uses a hwalcha (lever) to lift up heavy stones, and it greatly reduced the construction time.

 
  • 此外丁若镛发明的起重机使用了多个滑轮,能经很小的力气拉动沉重的石头,大大提高了工程的效率。
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