The plumb bob is then dropped, a distance of 20 ft. measured from it on the road, and a mark made.
A plumb bob must be attached exactly in the center of the tripod head.
When the instrument was level atop these rings, the plumb bob was theoretically over the center line of the cannon.
Our surveying apparatus was a triangle and a plumb bob which we made ourselves.
He thought that a plumb bob dropped through the long axis of the rocket would form a right angle with the surface of Arzachel.
He had a plumb bob in his hand and a spirit level, but he laid them down.
A protractor may be used in the same manner by sighting along the top and using a plumb bob to record the angle.