Explanation:
When operating a theodolite, the vertical circle is an important component that helps in measuring vertical angles. The vertical circle is usually located on the right side of the observer, but sometimes it may be on the left side due to various reasons such as previous adjustments or errors.

In order to bring the vertical circle to the right of the observer, if it is originally on the left, or vice versa, the operation is called "Changing Face".

Steps to perform Changing Face:
1. Lock the telescope: Before performing any adjustments, the telescope should be locked securely to prevent any movement.
2. Release the lower clamp: The lower clamp should be released to allow the telescope to move freely.
3. Rotate the telescope: Rotate the telescope horizontally until the vertical circle comes to the desired side (right or left).
4. Lock the lower clamp: Once the vertical circle is on the desired side, the lower clamp should be tightened to hold the telescope in place.
5. Check for level: After changing the face, it is important to check if the instrument is still level. Use the bubble level to ensure that the theodolite is properly leveled before proceeding with further measurements.

Importance of Changing Face:
Changing face is important in theodolite operations because it allows the observer to have a clear view of the vertical circle. The vertical circle is used to measure vertical angles accurately, and having it on the right side (as conventionally preferred) provides better visibility and ease of use.

Conclusion:
In conclusion, the operation of bringing the vertical circle to the right of the observer, if it is originally to the left, or vice versa, is called "Changing Face". This operation is performed by releasing the lower clamp, rotating the telescope, and then locking the lower clamp again. Changing face is important to ensure that the observer has a clear view of the vertical circle and can accurately measure vertical angles.