The use of derivatives in geomorphometry is reviewed. For first and second derivatives (slope and curvatures) of the land surface, represented by a square-grid DEM, use of a quadratic based on nine points is recommended. For detailed analysis of slope gradient, maximum slope (based on two points) may be useful: but only if the DEM is very accurate. For curvature, streamline (rotor) curvature should be added to profile and plan curvature. The system of local point-based variables in the gravity field is now extended to third derivatives.