| 摘要 |
A transparent plumb bob having a fixed point and an associated movable point, to be aligned therewith for determination of a vertical line through a given exterior point, optionally including means for horizontal leveling and easily securing the bob intermediate the ends of a string. A vertical or horizontal line is determined by fixing one string end to a point spaced from the plumb bob and then pivoting the plumb bob and other string end about the point until the associated indicators are in alignment.
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