Correct Answer - Option 4 : When the traverse is so short that accumulated errors in carrying the azimuth forward might be greater than orientation by compass.
Orientation of plane table by trough compass:
The compass, though less accurate, often proves a valuable adjunct in enabling the rapid approximate orientation to be made prior to the final adjustment. The plane table can be oriented by compass under the following conditions final adjustment.
- When speed is more important than accuracy
- When there is no second point available for orientation
When the traverse is so long that accumulated errors in carrying the azimuth forward might be greater than the orientation of the compass
- For approximate orientation prior to final adjustment.