  Both high resolution spectra of QSOs observed at the 8-10m telescopes and
advanced methods of data analysis are crucial for accurate measurements of the
chemical composition and physical parameters of the intervening clouds. An
overview of our recent results obtained with the Monte Carlo inversion (MCI)
procedure is presented. This includes: (1) variations of the shape of the local
background ionizing continuum in the 1-5 Ryd range at redshift z ~ 2.8-3.0; (2)
an inverse correlation between the measured metallicity, [C/H], and the
absorber line-of-sight linear size, L; (3) a functional dependence between the
line-of-sight velocity dispersion, sigma_v, and L.
