Since woven glass PCB substrates are anisotropic, EDA design and modeling software hoping to advance AI and ML algorithms should have provisions to model anisotropic material, especially via transitions. In this article, Bert Simonovich discusses the importance of having an awareness of the test method used by CCL suppliers for accurate modeling and simulation. Simonovich covers how the use of out-of-plane Dkz values instead of in-plane Dkxy values for via modeling can cause misleading simulation results, which may result in reduced margins and potential compliance test failures when the design is built and tested.