Inspecting 3d scanned machined surface for flatness?

[threedachs2]

Hello, I am a retired engineer just starting to use a 3d scanner for my hobbies.  I have been using the free version of Fusion to post-process the scans but, have a lot to learn.  I did a 3d scan of a machined part and would like to evaluate the flatness of a machined surface.  Ideally, I would like to have a contour plot of the surface showing high and low areas.  Is that something Fusion can do?  If not, is there any other software, preferably free, that you can recommend that can?  Thanks for any help you can provide.