In previous sections of this book, we have discussed machinery diagnostics from the point of view of conventional bearing technology. The technology continues to evolve, and new bearing developments promise to change the behavior of machines and the way we look at machinery data. The externally pressurized bearing is undergoing rapid development, and, because of its external pressure source, it has the capability of producing variable spring stiffness under operator or automatic control. As the externally pressurized bearing enters general use, it promises to change rotor behavior in ways that will affect diagnostic methodology.