Quarks interact weakly at high energies, allowing perturbative calculations. The FRGE is an exact equation without any perturbative approximations. When calculating the fluctuations with a perturbative approach, the zero order approximation is Fick's law. However, it was found to be a regularization suitable also for perturbative calculations. A Feynman diagram is a graphical representation of a perturbative contribution to the transition amplitude. The Virial equation derives from a perturbative treatment of statistical mechanics. This is because perturbative calculations are done in the interaction picture. So far we have neglected the fact that the deformation itself creates a perturbative potential. In two dimensions, the perturbative expansion parameter is 2/3. The deformation was created by the a perturbative potential of size formula 74. The perturbative treatment of the Stark effect has some problems. Exact and perturbative results can thusly be analyzed for several models of disorder.