RE: correct bias usage and using "Search the TASS Site"

[<aah@nofs.navy.mil>]

Yes, if the exposure times are the same, you don't need to
subtract bias since bias is included in both the frame in
question and the dark frame.  Note that we don't yet have a true bias
anyway; Tom's shortest exposure is ~40sec long, not zero sec.
That is one reason why I asked him for overscan columns.
  If exposure times are not equal, you need to scale dark,
and you can't scale dark without subtracting a true bias.
  If TEC temperatures are not equal, then you need to
also scale dark, but temperature difference scales as a power and not linear.
That is one reason why to look at the dark columns, if
they are truely dark columns.
  So, for the time being, it is easier to take darks of
the same exposure time and subtract such a mean dark from the
flat.  Then, normalize (flat-dark) using your median center box
so that all flats are at the same level.  Then median filter to
remove stars, etc.
Arne