  The numerical computation of reliable and accurate Stokes profiles is of
great relevance in solar physics. In the synthesis process, many actors play a
relevant role: among them the formal solver, the discrete atmospheric model,
and the spectral line. This paper tests the performances of different numerical
schemes in the synthesis of polarized spectra for different spectral lines and
atmospheric models. The hierarchy between formal solvers is enforced, stressing
the peculiarities of high-order and low-order formal solvers. The density of
grid points necessary for reaching a given accuracy requirement is
quantitatively described for specific situations.
