Variability stands in the way of delivering consistent product quality from microwave ovens. A good microwave product developer takes into account all the sources of variability in the test system that an end user may see. The two largest sources of variability are the differences in microwave ovens in the marketplace and the end users themselves. This chapter outlines a test procedure that aids the developer in determining the robustness of a product/package design and if an applied fix improves performance in all of the variability found in the marketplace.