  The basic parameters of supersymmetric theories can be determined at future
e^+e^- linear colliders with high precision. We investigate in this report how
polarisation measurements in \tilde{\tau} and \tilde{t} or \tilde{b} decays to
\tau leptons and t quarks plus neutralinos or charginos can be used to measure
\tan\beta (in particular for large values) and to determine the trilinear
couplings A_{\tau}, A_t and A_b in sfermion pair production.
