短語詞組短語plumb -line mean flow velocity 垂線平均流速Plumb -bob line 鎚線local plumb -line variation 地方鉛垂線變化direction of plumb -line 垂線方曏correction for plumb -line curvature 垂線曲率改正digital plumb -line tele-coordinator 遙測垂線儀 返回 plumb-line