Setting up a plane table at a station: Which operation is carried out first in correct field procedure before others such as levelling and orientation?

Introduction / Context:
Proper setup of a plane table ensures that plotted positions correspond to ground positions. The standard sequence is important: if you level or orient before the table is actually over the station, your subsequent work is mislocated and must be redone.

Given Data / Assumptions:

• Station point on ground is marked (peg, nail, or station mark).
• Plane table with plumbing fork or centering device is used.
• All three operations—centering, levelling, orientation—must be completed.

Concept / Approach:
Centering places the table exactly above the ground station so that the drawing sheet’s station point is co-vertical with the ground point. Levelling then ensures the alidade operates in a horizontal plane. Orientation matches the table's directions with the field. If you do not center first, subsequent steps are wasted because the board would have to be moved again, disturbing level and orientation.

Step-by-Step Solution:

Verification / Alternative check:
Some field crews do quick rough levelling during centering just to ease adjustments, but the formal precedence is centering → levelling → orientation.

Why Other Options Are Wrong:

• Levelling first: You will disturb level when you later shift the board for centering.
• Simultaneous: Not reliable; centering must come first.
• Orientation first: Impossible until the board is centered and levelled.

Common Pitfalls:
Neglecting to re-check level after final orientation; minor rotations can throw off levelling.

Final Answer:
Centering the board over the station first