  In the past years we have made great efforts to reduce the statistical and
systematic uncertainties in stellar parameter and chemical abundance
determinations of early B-type stars. Both the construction of robust model
atoms for non-LTE line-formation calculations and a novel self-consistent
spectral analysis methodology were decisive to achieve results of unprecedented
precision. They were extensively tested and applied to high-quality spectra of
stars from OB associations and the field in the solar neighbourhood, covering a
broad parameter range. Initially, most lines of hydrogen, helium and carbon in
the optical/near-IR spectral range were reproduced simultaneously in a
consistent way for the first time, improving drastically on the accuracy of
results in published work.By taking additional ionization equilibria of oxygen,
neon, silicon and iron into account, uncertainties as low as ~1% in effective
temperature, ~10% in surface gravity and ~20% in elemental abundances are
achieved - compared to ~5-10%, ~25% and a factor ~2-3 using standard methods.
  Several sources of systematic errors have been identified when comparing our
methods for early B-type stars with standard techniques used in the nineties
and also recently (e.g. VLT-FLAMES survey of massive stars). Improvements in
automatic analyses are strongly recommended for meaningful comparisons of
spectroscopic stellar parameters and chemical abundances ('observational
constrains') with predictions of stellar and galactochemical evolution models.
