Central structure diameter (Cd). Value is actually diameter of a circle with an area equivalent to that encompassing any central structure; measured in the same manner as rim-to-rim diameter. Previous studies have measured peak ring diameter by fitting a circle to the peaks of the ring massif (e.g., Pike and Spudis 1987, EM &P, v. 39, 129). For the sake of interplanetary comparisons in the text we also used this older technique to measure peak ring diameters for single- and double-ring basins. Peak ring diameters using this second technique is in the separate sheet. Error for central peak or peak ring diameter using the equivalent area technique is 6%. Error for peak ring diameter using the circle-fitting technique is 1.7 km.