This demonstration is similar to the various demos on Gaussian curvature in that there is a square patch in the "Domain" window that can be moved around and resized using the two hotspots. The patch is color-coded and its image apears on the surface in the "Torus" window.
The window "Mean Curvature Graph H(u,v)" displays a graph of the mean curvature of the surface at each point in the domain. The graph of H(u,v) is colored using a gradient so that the graph is blue whenever H(u,v) < 0, white whenever H(u,v) = 0, and red whenever H(u,v) > 0. This coloring scheme makes it easy to tell whether a surface is minimal.