  Multi-object and multi-fiber spectrographs on 4 and 8 meter telescopes make
it possible to use extragalactic planetary nebulae (PNe) in the outer halos of
early-type galaxies as kinematical tracers, where classical techniques based on
integrated stellar light fail. Until now, published PNe radial velocity samples
are small, with only a few tens of radial velocity measurements (except for a
few cases like NGC 5128 or M31), causing uncertainties in the mass and angular
momentum estimates based on these data. To quantify these uncertainties, we
have made equilibrium models for spherical galaxies, with and without dark
matter, and via Montecarlo simulations we produce radial velocity samples with
different sizes. We then apply, to these discrete radial velocity fields, the
same standard kinematical analysis as it is commonly done with small samples of
observed PNe radial velocities. By comparison of the inferred quantities with
those computed from the analytical model, we test for systematic biases and
establish a robust procedure to infer the angular momentum distribution and
radial velocity dispersion profiles from such samples.
