Abstract: An apparatus and method for locating the vertical axis of symmetry of a sace of horizontal circular cross-section. The apparatus has a plumb structure that establishes a vertical line of sight, and a horizontal translating structure that preselectedly locates the plumb in the two horizontal dimensions. The plumb has at least three arms whose ends are constrained to lie on a circular perimeter which, because the arms are fixed to the plumb, is horizontally disposed. The translating structure and the arms are manipulated so that the end of the arms touch the surface, constraining the line of sight to be colinear with the axis of symmetry. A laser can make the axis visible. The apparatus and method are useable to locate the focal axis and focus of a parabolic antenna.