Which of the following is NOT the error due to manipulation and sighting in plane table survey?

Concept:

The errors in plane table surveying are of three types :

1. Instrumental errors: These are:

• Sight vane and object vane of alidade is not perpendicular
• The edge of the alidade is not straight or curved.
• Loose fittings of the tripod and plane table.
• The top surface of the plane table is not flat.
• Faulty spirit level

2. Errors in plotting: These are:

• Use of poor-quality drawing papers.
• Expansion or contraction of drawing paper against temperature changes. 
• The wrong scale of the drawing.
• Use of very thick pencil.

3. Errors due to manipulation and sighting (personal errors or man-made errors):

• Improper clamping of a tripod.
• The drawing sheet of the plane table is not firmly fixed.
• Centering error - the plane table is not exactly over the ground point.
• Improper orientation of plane table.
• Improper sighting through vanes causes errors in direction of the object.