So, a customer has asked for the flatness of some of their products to be checked after they were found to be quite bent. Unfortunately their drawing only calls for surface profile. It's a relatively straight edge, so I was thinking of either creating a plane from already programmed points to create flatness, or using the already called out profile for the points to work out the flatness.
How much/little is "quite bent?" If it's on the order of 0.0001" or greater, wouldn't a good dial indicator and base, together with a granite surface plate suffice?. If the deviations are a lot smaller, you might consider checking the surfaces visually with an optical flat and (near) monochromatic light, say from a sodium-vapor lamp, and counting fringes.
Are you looking for a way to calculate flatness, represent flatness, measure flatness, or correct it?
For measuring, the above seem to be the go-to. A heightmap of points and a little visualization does wonders for demonstrating it, but depending on the kinds of features and requirements of the part, a meaningful measurement for it has to be picked from a variety of potential representations.