The infrared flux method is a semi-direct technique developed
by Blackwell & Shallis (1977) for cool stars, which uses the ratio
of the integrated flux relative to a monochromatic IR flux to obtain a
star's angular diameter and 
using an iterative
procedure based on model atmospheres. Napiwotzki et al. (1993) found that
the V-band flux provided an better
calibration for B, A and F stars.
Fitting model spectra to observations over the entire
spectral range provides improved results for B stars
(e.g. Malagnini et al. 1986; Drilling et al. 1984).
Temperatures for DB white dwarfs
can be obtained from UV continuum fits (e.g. Thejll et al. 1991),
while hotter stars tend to be poorly constrained
(e.g. `R-index' technique of Schönberner & Drilling 1984),
often suffering the added complication of varying
UV interstellar extinctions from star to star.
Figure: Kurucz (ATLAS9) theoretical energy distributions
for B0--A0 dwarfs
showing the strong temperature sensitivity of the Balmer jump,
measured by the Strömgren colour-indices [
] (favoured
below 
20kK) and [u-b] (above 
20kK)