Spirit Level

Circular spirit level is used for check the level of the board and make it horizontal by placing it on the board in two positions mutually at right angles and centering the bubble in each position.

Plumbing Fork

It is also called as U frame. It is a hairpin shaped brass frame having two arms of equal length as depicted in Figure 2(b). A single end of the frame is pointed and is kept over the drawing sheet touching the plotted position of the instrument station. Another end of the frame carries a plumb bob. The situation of the plane table is adjusted until the plumb bob hangs over the station occupied through the instrument.