Plumbing Fork and Plumb Bob

Given figure indicate a typical plumbing fork with a plum bob. Plumbing fork is a U-shaped metal frame having a lower inclined arm and upper horizontal arm. The upper arm is provided having a pointer at the end whereas the lower arm is provided with a hook to suspend plumb bob. On the plane table when the plumbing fork is kept the vertical line (line of plumb bob) passes through the pointed edge of upper arm. Plumb bob helps in transferring the ground point to the drawing sheet and also vice versa.

                    Plumbing fork  and plumb bob.

A flat based spirit level is used to level the plane table during surveying as shown in figure. To get perfect level Spirit level should show central position for bubble tube when checked with its positions in any two mutually perpendicular directions.

                             Spirit level