The axial accuracy of a photoelectric theodelite greatly determines the measuring accuracy of the whole instrument. Taking the photoelectric theodolite GD-220 as an example

this paper discusses various kinds of errors in the vertical and horizontal axial systems i.e. radial runout

angular swing and axial shifting

and quantitatively analyzes the axial swing error caused by the surface figure error and position error of the axial system parts. The measured results of 9 sets of GD-220 photoelectric theodolites are listed

showing that the analysis of the axial accuracy and structure design of the axial system are both reasonable.