Hey, you need to reparameterize the Srf. You're running into the problem described on p. 86 in the primer, where you need to reset the domain of the surface to be between 0 and 1 :)
Hi Tom, I made a solution for your diagrid tower, based on the curves of the primer page 84 curves. If that is also what your mesh is based on (or somethin similar), this will work nicely.