| 摘要 |
A first rod includes a relative elevation scale and a first fluid container vertically adjustable with respect to the relative elevation scale to a position corresponding to a desired elevation relative to the base of the first rod, and a second rod includes a second fluid container of substantially lesser cross sectional area than the first fluid container, a predetermined level of fluid in the second fluid container indicating that the base of the second rod is at a desired elevation relative to the base of the first rod.
|
