A lack of symmetry in the appear-ance of an object as seen from a particular point of observation, and caused by an actual asymmetry in the object or its aspect. It causes an object to appear differently when viewed from different points and can result in different points of the object being sighted at from different points of observation. A square or rectangular pole may face the observer in such a way that a line bisecting the angle made by lines of sight tangent to the pole's edges does not pass through the centre of the pole. If, instead of a pole, a square cupola or tower is sighted on, the error may be quite large. The error caused by observing on such objects is of the same character as the error caused by observing an eccentric object. Asymmetry of object differs from phase in that the former is caused by an actual asymmetry of the object as viewed; the latter is caused by an asymmetric illumination of the object.