Global versus local billiard level dynamics: The limits of universality

Level dynamics measurements have been performed in a Sinai microwave billia rd as a function of a single length, as well as in rectangular billiards wi th randomly distributed disks as a function of the position of one disk. In the first case the field distribution is changed globally, and velocity di stributions and autocorrelation functions are well described by universal f unctions derived by Simons and Altshuler. In the second case the field dist ribution is changed locally. Here another type of universal correlation is observed. It can be derived under the assumption that chaotic wave function s may be described by a random superposition of plane waves.