  We present a numerical study of the evolution of a non-linearly disturbed
black hole described by the Bondi--Sachs metric, for which the outgoing
gravitational waves can readily be found using the news function. We compare
the gravitational wave output obtained with the use of the news function in the
Bondi--Sachs framework, with that obtained from the Weyl scalars, where the
latter are evaluated in a quasi-Kinnersley tetrad. The latter method has the
advantage of being applicable to any formulation of Einstein's
equations---including the ADM formulation and its various descendants---in
addition to being robust. Using the non-linearly disturbed Bondi--Sachs black
hole as a test-bed, we show that the two approaches give wave-extraction
results which are in very good agreement. When wave extraction through the Weyl
scalars is done in a non quasi-Kinnersley tetrad, the results are markedly
different from those obtained using the news function.
