How to Read a Plumb Bob

The plumb bob is an ancient tool used that is still used in construction.

The plumb bob is one of the simplest and oldest construction tools still in use today. A plumb bob is nothing more than a weight hanging on the end of a string. It is used to establish true vertical since, when the weight is suspended from the string, it always hangs in the direction of gravity. Although plumb bobs are more precisely balanced now than their ancient counterparts, in all other respects, the plumb bob has remained unchanged for thousands of years.

Things You'll Need

• Plumb bob
• String
• Ruler

Instructions

1. Tie the plumb bob to a string. According to Bobvila.com, you can use either cotton or nylon string. Nylon is more resistant to moisture.

2. Attach the string next to or in front of the object you wish to plumb. If you wish to plumb a doorway, for example, hang the plumb bob next to the corner of the doorway. Alternately, hang the plumb bob in front of the object you want to plumb. For example, if you wish to see if a fence post veers left or right, hang the plumb bob in front of it.

3. Wait for the plumb bob to stop swinging and hang perfectly still. A plumb bob is a long pendulum and can take several seconds to become completely still.

4. Sight the plumb line (the line made by the string of the plumb bob) against the item you want to plumb.The plumb line should be the same distance from the object the whole way down if the object is straight. If the plumb bob is in front of the thing you are plumbing, both the top and the bottom of the plumb bob should be directly in front of the object if it is true. If the plumb bob seems to veer to the side, towards or away from the object, the object is not vertical.

5. Confirm your sighting with a measurement. If you are plumbing a doorway, for example, measure the distance between the string and the frame at the top of the doorway. Measure the same distance at the point where the string joins the bob. If the distances are equal, the doorway is straight.

References

• BobVila.com: The Plumb Bob
• DoItYourself.com: Plumb Bob