假设这是铅垂。，想想重力方向是怎样的。
Think of this as being a plumb line to find... used to find the direction of gravity.
其他必须的工具包括米尺，铅垂和罗盘。
Additional tools which will be required are metre stick plumb line and compass.
建立了铅垂油井杆管偏磨临界轴向压力的计算公式。
The calculating formula for critical axial load of worn rod string and tubing was set up.
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