試敘述用測回法測量水平角的步驟?

(1)對中整平儀器后，正鏡瞄準后視點，讀取水平度盤;

(2)正鏡順時針方向旋轉照準部，照準前視點，讀取水平角度盤;

(3)倒鏡后逆時針旋轉照準部，照準前視點，讀取水平角度盤;

(4)倒鏡逆時針旋轉照準部，照準后視點，讀取水平角度盤;