Short Answer:

To set up a plane table, first fix the table on a tripod and place it over the selected ground point. Use a plumb bob or plumbing fork to center the table exactly above the station mark. Then, use a spirit level to ensure the board is completely horizontal. Once centered and leveled, fix a drawing sheet firmly on the table using clips or tacks.

After that, the table needs to be oriented—this means aligning the table with a reference direction (usually north or a previously plotted line). Now, the table is ready for surveying work like sighting and plotting points.

Detailed Explanation:

Set up a plane table

Setting up a plane table is the first and most important step in plane table surveying. Proper setup ensures that all further measurements and drawings are accurate. The process involves selecting a ground station, placing the table properly over it, leveling it, and aligning it in the correct direction. A well-set plane table provides a stable base for drawing and observing, helping surveyors record accurate field details.

Steps to set up a plane table:

1. Fixing the plane table on the tripod
   Start by attaching the plane table firmly onto the tripod. Make sure it is screwed tightly so that it does not move during work. The tripod should be placed approximately over the survey station.
2. Centering the table
   Centering means placing the plane table exactly above the ground point or station mark. Use a plumbing fork and plumb bob for this:

• Place the plumb bob below the hole in the plumbing fork.
• Move the tripod slightly until the plumb bob points exactly to the ground mark.
• Once centered, do not move the tripod again.

3. Leveling the table
   Leveling is done using a spirit level. Place the spirit level in the center of the table and adjust the tripod legs or use leveling screws to make the bubble stay in the center. Repeat this in multiple directions (two or more sides) until the entire table is horizontal.
4. Fixing the drawing sheet
   Attach the drawing sheet using clips, tacks, or tape. The sheet should be clean, flat, and tightly fixed to prevent it from moving during drawing or sighting. Mark the reference point on the sheet to match the ground station.
5. Orientation of the table
   This step involves rotating the table to match the direction of the previous station or to align with magnetic north:

• If using a compass, place it on the table and rotate the board until the north of the compass matches with the north on the sheet.
• If aligning with a previously drawn line, sight the same object again using an alidade and rotate the board until the sighting line matches the drawn line.

6. Final check
   Once centered, leveled, and oriented, check again to ensure everything is correct. The table must remain steady, flat, and correctly aligned before beginning the survey.

Why proper setup is important:

• Ensures correct angular readings using the alidade.
• Maintains accuracy in drawing and distance plotting.
• Helps in repeating orientation correctly at multiple stations.
• Prevents cumulative errors in the map.

Tips for smooth setup:

• Choose firm and level ground for setting the tripod.
• Avoid windy areas or protect the sheet from flapping.
• Double-check orientation before starting observations.

Conclusion

Setting up a plane table involves fixing it on a tripod, centering it with a plumb bob, leveling it using a spirit level, and orienting it correctly using a compass or alidade. A stable, properly set table is essential for accurate and efficient plane table surveying.