  We present the recent results of a research project aimed at constructing a
robust wave extraction technique for numerical relativity. Our procedure makes
use of Weyl scalars to achieve wave extraction. It is well known that, with a
correct choice of null tetrad, Weyl scalars are directly associated to physical
properties of the space-time under analysis in some well understood way. In
particular it is possible to associate $\Psi_4$ with the outgoing gravitational
radiation degrees of freedom, thus making it a promising tool for numerical
wave--extraction. The right choice of the tetrad is, however, the problem to be
addressed. We have made progress towards identifying a general procedure for
choosing this tetrad, by looking at transverse tetrads where $\Psi_1=\Psi_3=0$.
  As a direct application of these concepts, we present a numerical study of
the evolution of a non-linearly disturbed black hole described by the
Bondi--Sachs metric. This particular scenario allows us to compare the results
coming from Weyl scalars with the results coming from the news function which,
in this particular case, is directly associated with the radiative degrees of
freedom. We show that, if we did not take particular care in choosing the right
tetrad, we would end up with incorrect results.
