plumb-line observer垂线观测仪
plumb-line e铅垂线
plumb ĥ line铅垂线
plumb-line sign垂直线征英语;垂直线征;翻译
plumb b line铅垂线
plumb-line垂线
local plumb-line variation地方铅垂线变化
direction of plumb-line垂线方向
plumb-line mean flow velocity垂线平均流速
N-COUNT（可数名词） A plumb line is a piece of string with a weight attached to the end that is used to check that something such as a wall is vertical or that it slopes at the correct angle. 铅垂线