(1) The change (δg _c) in the calculated value of gravity, on the reference surface, when matter in the form of a thin disk, radius r at depth D below that surface is removed. The matter in the disc is used, after applying a free air gravity correction, to fill the Bouguer cylinder. The mass M in the Bouguer cylinder is given by M = ρπr²h, in which h is the height of the cylinder, r the radius and ρ the density of the matter in it. The change δg _c (in newtons per kilogramme or metres per second²) is δg _c = 2GM (((h+D)/ √(r ² +(h+D)²) - 1)/r ², in which G is the gravitational constant. (2) The same as the preceding definition but with elevation H being used instead of height h, the geoid being used as the reference surface. (3) The same as either of the preceding definitions, but with the condensed mass lying in a thin layer on a surface parallel to the reference surface and equal to the topographic masses outside that surface.