When a gantry crane of China Shipbuilding is moving, its two feet slide along tracks, and every 50 meters the crane operators have to check to see if the crane is moving straight.
而中船的門形吊車移動時，兩隻座腳則在輪軌上滑動，吊車手每五十公尺就要檢查有沒有「斜行」。