Plumb-bob

For the nuclear testing program, see Operation Plumbbob

Plumb Bob

A plumb-bob is a weight with a pointed tip on the bottom that is suspended from a string and used as a reference line that is perpendicular to the ground.

This instrument has been used since the time of the ancient Egyptians by bricklayers, masons, and carpenters to ensure that their constructions are "square", or perfectly upright. It may also be used in surveying to sight a point on the ground that is not readily visible.

Usage

To mark a vertical line on a wall, the following procedure may be used:

The plumb-bob is hung from a chalk-coated string almost against the wall (ideally with a tiny gap). A nail or other device is used to secure the string at the top, near the wall.
The weight may swing and/or twirl dramatically at first, it can be steadied most of the way by hand.
The weight is left to find its final position (this may take quite some time).
Once the weight comes to rest in its final position, it may be held against the wall and the string "snapped" against the wall. This will create a vertical chalk line.
The chalk line may be removed when no longer needed.

References

[60 oz. Plumb Bob].

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