The primary source of instrumental errors in plane table surveying arise from the lack in temporary adjustment. Thus, the causes for instrumental errors are as follows :
(i) Undulated plane table surface : Error in observation as well as plotting will occur if the top surface of the plane table is not perfectly plane.
(ii) Curved or inclined fiducial edge : If the fiducial edge of the alidade is not straight, the rays drawn would not be straight and an error in relative location of object will occur.
(iii) Loose fittings in plane table : If the fittings of the plane table and that of tripod are loose, the plane table will not remain stable and error in surveying will occur.
(iv) Improper magnetic compass: If the magnetic compass is sluggish or does not represent proper magnetic direction, an error in orientation of the plane table will occur, (if it is done with the magnetic compass) and thus basic principle of plane table surveying will get violated.
(v) Non-perpendicularity of the sight vanes : If the sight vanes are not perpendicular to the base of the alidade, there would be an error in sighting.
(vi) Defect in level tube: If the level tube is defective, the plane table will not be horizontal when the bubble is central. The plot thus obtained will be inaccurate.
(vii) Unseasoned, poor quality drawing paper : Poor quality drawing paper gets affected by the weather changes and thus it may expand or contract and changes the scale of plotting. The plot thus obtained will be incorrect.