  We re-analyse the ASCA and GINGA X-ray data from BY Cam, a slightly
asynchronous magnetic accreting white dwarf. The spectra are strongly affected
by complex absorption, which we model as a continuous (power law) distribution
of covering fraction and column of neutral material. This absorption causes a
smooth hardening of the spectrum below 3 keV, and is probably produced by
material in the preshock column which overlies the X-ray emission region. The
ASCA data show that the intrinsic emission from the shock is not consistent
with a single temperature plasma. Significant iron L emission co-existing with
iron K shell lines from H and He-like iron clearly shows that there is a wide
range of temperatures present, as expected from a cooling shock structure. The
GINGA data give the best constraints on the maximum temperature emission in the
shocked plasma, with kT(max)=21(+18,-4) keV. Cyclotron cooling should also be
important, which supresses the highest temperature bremsstrahlung components,
so the X-ray data only give a lower limit on the mass of the white dwarf of M>
0.5 solar masses. Reflection of the multi-temperature bremsstrahlung emission
from the white dwarf surface is also significantly detected.
  We stress the importance of modelling ALL these effects in order to gain a
physically self-consistent picture of the X-ray spectra from polars in general
and BY Cam in particular.
