  The Sunyaev-Zel'dovich (SZ) effect of galaxy clusters is characterized by
three parameters: Compton parameter, electron temperature and cluster peculiar
velocity. In the present study we consider the problem of extracting these
parameters using multi-frequency SZ observations only. We show that there
exists a parameter degeneracy which can be broken with an appropriate choice of
frequencies. As a result we discuss the optimal choice of observing frequencies
from a theoretical point of view. Finally, we analyze the systematic errors (of
the order micro K) on the SZ measurement introduced by finite bandwidths, and
suggest a possible method of reducing these errors.
