Global and local level dynamics in chaotic microwave billiards

The spectra of Sinai microwave billiards and rectangular billiards with sta tistically distributed circular scatterers have been taken as a function of the position of one wall, and of one of the scatterers, respectively. Wher eas in the first case the velocity distribution and correlations obey the u niversal behaviour predicted by Simons and Altshuler, in the second case a completely different behaviour is observed. This is due to the fact that a shift of one wall changes the wave function globally whereas the displaceme nt of one scatterer only leads to a local perturbance.