  We report a significant finding in Quintessence theory that the the scalar
fields with tracker potentials have a model-independent scaling behaviour in
the expanding universe. So far widely discussed exponential,power law or
hyperbolic potentials can simply mimic the tracking behaviour over a limited
range of redshift. In the small redshift range where the variation of the
tracking parameter $\epsilon$ may be taken to be negligible, the differential
equation of generic potentials leads to hyperbolic sine and hyperbolic cosine
potentials which may approximate tracker field in the present day universe. We
have plotted the variation of tracker potential and the equation of state of
the tracker field as function of the redshift $z$ for the model-independent
relation derived from tracker field theory; we have also plotted the variation
of $V(\Phi)$ in terms of the scalar field $\Phi$ for the chosen hyperbolic
cosine function and have compared with the curves obtained by reconstruction of
$V(\phi)$ from the real observational data from the supernovae.
