  The topic of magnetic field diagnostics with the Zeeman effect is currently
vividly discussed. There are some testable inversion codes available to the
spectropolarimetry community and their application allowed for a better
understanding of the magnetism of the solar atmosphere. In this context, we
propose an inversion technique associated with a new numerical code. The
inversion procedure is promising and particularly successful for interpreting
the Stokes profiles in quick and sufficiently precise way. In our inversion, we
fit a part of each Stokes profile around a target wavelength, and then
determine the magnetic field as a function of the wavelength which is
equivalent to get the magnetic field as a function of the height of line
formation.
  To test the performance of the new numerical code, we employed "hare and
hound" approach by comparing an exact solution (called input) with the solution
obtained by the code (called output). The precision of the code is also checked
by comparing our results to the ones obtained with the HAO MERLIN code. The
inversion code has been applied to synthetic Stokes profiles of the Na D$_{1}$
line available in the literature. We investigated the limitations in recovering
the input field in case of noisy data. As an application, we applied our
inversion code to the polarization profiles of the Fe {\sc i} $\lambda$ 6302.5
\AA\ observed at IRSOL in Locarno.
