Question

The instrument used for accurate centering in plane table surveying is :

• A. Plumbing fork
• B. Alidade
• C. Spirit level
• D. Trough compass

Answer 1

The correct option is A Plumbing fork

Plumbing fork: It is used for the centering of the table over the station.



Note:

1. Level Tube/Spirit Level

Level tube/spirit level is used for levelling the plane table.

It is placed on the board in two positions mutually at right anlages and the bubbles is centered in arch position to make the board horizontal.

2. Trough Compass

Generally it is 15 cm long and is provided to plot the magnetic meridian (N-S direction) to facilitate orientation of the plane table in the magnetic meridian.



3. Alidade

An alidade is a straight - edge ruler having some sighting device. It is used for sighting the object and drawing the line.

Now a days telescopic alidade are also much is use in place of plane alidade. When the point is too high or low are to be sighted, the accuracy and the range are considerably increased by providing a telescopic alidade.

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