Black Friday: lifetime access is on a special offer in the app, until November 30. Black Friday: special offer on lifetime access, until November 30. Download
홍수계는 강의 수위를 측정하는 데 사용됩니다.Hongsugye-neun gang-ui suwi-reul cheugjeonghaneun de sayongdoemnida.The flood gauge is used to measure the water level of the river.