A plumb bob is used to transfer points from below or above a pre-determined point so that they are in vertical alignment. A plumb bob consists of a weighted piece attached to a long string. To use a plumb bob, mark the spot above the area you are creating a vertical line to, wrap the plumb bob string around a nail or other object and lower the plumb bob until it is very close to the working surface but not touching. When the plumb bob stops swinging, the pointed end of the plumb bob will be exactly in line with the point above. The two points are in perfect vertical alignment.
Unscrew the removable top at the end opposite the pointed end of the plumb bob.
Feed the plumb bob dry line or string through the hole in the removable top. The line should be at least the height from floor to ceiling; 8 feet is typical.
Tie a double knot in the end of the string. Pull the remaining string through the plumb bob top until the knot sits inside the removable cap.
Replace the cap on the weighted and pointed end of the plumb bob.