Since our nominal system was simply a planar wavefront passing through a perfectly planar slab of glass, the wavefront error was initially zero, and thus the criteria is equivalent to the change in criteria in the tolerance output.  On average, the inhomogeneity of the glass resulted in nearly a quarter wave RMS wavefront error.  We can evaluate each wavefront profile by individually opening each of the saved Monte Carlo files and reviewing the Wavefront Map.  Nominally, our wavefront had no variation across the pupil:



Yet after the randomly chosen Zernike coefficients from the tolerance analysis, the wavefront is clearly aberrated, or “warped.”



Each Monte Carlo trial will have a slightly different representation of the inhomogeneity of your glass.  Therefore, a statistical listing of the entire Monte Carlo set is essential for estimating the probable effects the inhomogeneity has on your system performance.