Changes in cup anteversion on the C-arm monitor depends on the angle of incidence of the radiation; (a) Optimal angle of incidence of fluoroscopy; (b), (c) Sagittal malrotation of the C-arm; a′, b′, c′, Each vertical length of the obturator foramina on the monitor a, b, and c; (d), (e) Axial malrotation of the C-arm; R, L, Each width of the obturator foramina on the right and the left side.