Peter, Dennis,
FWIW, here is a good laymans overview of the whole process
that I keep as a bookmark for self reference every now and then.
It's easily forgotten by me over months and years and so a
good refresh every now and then is very helpful.
It mentions not only Flats but also Dark flats towards
the bottom.
http://www.aavso.org/observing/progr...manual/3.shtml
Steve