  Balmer lines are an important diagnostic of stellar atmospheric structure,
since they are formed at a wide range of depths within the atmosphere. The
different Balmer lines are formed at slightly different depths making them
useful atmospheric diagnostics. The low sensitivity to surface gravity for
stars cooler than ~8000 K makes them excellent diagnostics in the treatment of
atmospheric convection. For hotter stars Balmer profiles are sensitive to both
effective temperature and surface gravity. Provided we know the surface gravity
of these stars from some other method (e.g. from eclipsing binary systems), we
can use them to determine effective temperature.
  In previous work, we have found no significant systematic problems with using
uvby photometry to determine atmospheric parameters of fundamental (and
standard) stars. In fact, uvby was found to be very good for obtaining both
Teff and log g. Using Halpha and Hbeta profiles, we have found that both the
Canuto & Mazzitteli and standard Kurucz mixing-length theory without
approximate overshooting are both in agreement to within the uncertainties of
the fundamental stars. Overshooting models were always clearly discrepant. Some
evidence was found for significant disagreement between all treatments of
convection and fundamental values around 8000~9000K, but these results were for
fundamental stars without fundamental surface gravities. We have used stars
with fundamental values of both Teff and log g to explore this region in more
detail.
