(oi’ l∂r) A procedure applied to profile or gridded potential field data to solve Euler’s homogeneous equation (q.v.) for the locations and depths of sources for an assumed Euler structural index. On profiles, each calculation is run for a window length tuned to the expected depth range. With gridded magnetic or gravity maps, calculations are run over square windows that are moved by a grid unit for the next depth calculation. Pick values cluster together at a valid structural index; a fault might be indicated by a horizontal alignment. See Thompson (1982); Reid et al. (1990).