Setting up a Plane Table

A plane table is an instrument used for surveying and mapping purposes. It consists of a flat table or board with a leveling head and a sighting device. To set up a plane table at any station, the following steps are followed:

1. Levelling and Centering:

The first step is to level and center the plane table. This is done by adjusting the screws on the leveling head until the bubble in the spirit level is centered. The table is then placed on the tripod and leveled in all directions using the leveling screws on the tripod.

2. Orientation:

Once the table is level, it is oriented to the true north using a compass or a theodolite. The table is then clamped in position.

3. Sighting:

The next step is to sight the target using the sighting device. The surveyor looks through the sighting device and lines it up with the target. The position of the target is then marked on the table using a pencil or a pin.

4. Sketching:

After the position of the target is marked, the surveyor sketches the surrounding details on the table. This is done by sighting and marking the position of several other targets and drawing lines between them.

5. Calculation:

Once the sketch is complete, the surveyor calculates the position of the targets and other features using trigonometry and other mathematical calculations.

In conclusion, leveling and centering are done simultaneously while setting up a plane table. This is to ensure that the table is stable and accurate while sighting and sketching the targets.

Orientation & centering done simultaneously , Because while orientation is going on , it disturbing the centering therefore it is done simultaneously ....So correct answer for above question is Centering is done first ....