Effect of noise in the transverse field on the derived orientation of the vector field. (a) Black arrows represent the true vector field on the Sun (radial in this example). Red arrows represent the line-of-sight component and thick blue arrows are transverse components of the true vector field. Adding positive noise to the transverse field (thin blue arrows) makes the observed field (dashed arrow) systematically inclined in the direction away from the central meridian. Because of the 180° azimuthal ambiguity in the transverse field, the same transverse field may satisfy an alternative orientation (dashed-dotted arrow). The resulting orientation of the field vector is shown by a dashed arrow for both locations. Letters E, W, N mark approximate positions of solar East limb, West limb, and North as seen from Earth. (b) Difference between the true radial direction and vector orientation in the presence of noise, when azimuth disambiguation selects the most radial of two possible solutions (open circles). Solid line is a 6th degree polynomial fit.