**Sequence of Operations at Plane Table Station**

The correct sequence of operations at each plane table station is as follows:

**1. Levelling:**
The first operation to be performed at a plane table station is levelling. Levelling is the process of determining the height or elevation of a point relative to a reference point or datum. It is essential to ensure that the plane table is set up horizontally to avoid any errors in subsequent measurements.

During the levelling process, a spirit level attached to the plane table is used to check and adjust the horizontal position. The levelling screws on the tripod are adjusted to bring the bubble of the spirit level to the center. This ensures that the plane table is level and stable, providing a reliable base for accurate measurements.

**2. Orientation:**
Once the plane table is properly levelled, the next operation is orientation. Orientation refers to aligning the plane table with the true north direction or any other desired reference direction. This step is crucial for accurate plotting and mapping.

There are several methods to orient the plane table, such as using a magnetic compass or astronomical observations. The magnetic compass method involves aligning the magnetic needle of the compass with the magnetic north direction. Alternatively, astronomical observations can be made by sighting a known star or the sun to determine the true north direction.

**3. Centering:**
After the plane table is correctly oriented, the final operation is centering. Centering involves placing the plane table in the exact position over the point of interest or the station mark. This ensures that all subsequent measurements are relative to the desired reference point.

To center the plane table, the surveyor visually aligns the station mark or a plumb bob string with the corresponding point on the ground. The position of the plane table is adjusted by moving the tripod legs or using the centering screws until the desired alignment is achieved.

By following this sequence of operations (levelling, orientation, and centering), accurate and reliable measurements can be obtained during plane table surveying. These steps ensure that the plane table is set up correctly, aligned with the reference directions, and centered over the point of interest, enabling accurate mapping and plotting of the surveyed area.

Actually we go levelling and centering together hand in hand...