There are many ways to estimate quantitatively the roughness of terrains from topographic data. From the literature (Kreslavsky and Head, 1999, 2000; Rosenburg et al. 2011) and our own tests, we identified the Median Differential Slope (MDS) defined by Kreslavsky and Head (2000) as one of the most interesting roughness measures because of its high sensitivity to the geolo- gical nature of terrains. We concentrate on this particular criter- ion in this paper and show its variability among different terrains on a single planetary object and also the variation between different planets. In order to get a better understanding of the effects of differential slope calculations, we systematically com- pare the MDS curves with similar curves of absolute slope (Median Absolute Slope, MAS) and slope distribution at different baselines.