A rule relating the depth of a body to a feature of anomaly shape. Depth rules apply to specific anomaly source-body shapes; see Figure D-10. 1. Rules used in gravity interpretation include (a) half-width rules (the half-width being half the width at half the anomaly amplitude): for point masses: depth=1.3 half-width, and for horizontal line masses: depth=half-width. (b) For thin semi-infinite slabs and faults: half the width between points where the anomaly is one-quarter and three-quarters amplitude (see Figure H-1). 2. Rules used in magnetic interpretation include (a) the straight-slope-measurement rule (q.v.); (b) the Peters’ rule for dikes: depth=5/8 of the horizontal distance between points where the slope is half the maximum slope; (c) the Tiburg rule for magnetic poles: depth=2/3 of the horizontal distance at half the maximum amplitude; (d) the Hannel rule for magnetic poles: depth=half of the horizontal distance at a third the maximum amplitude; (e) the Thalen rule: the depth of a magnetic source is 0.7 the horizontal distance between maxima and minima; and other such rules. See also automated depth estimation and radial power spectrum.