Understanding sky-subtraction

[MarkDurre]

Hi, we are wanting to skip sky subtraction because of a complicated background field, but I don't quite understand the output files. From the documentation (DATA_PRODUCTS), there should be no difference between the "_ocubes" files with or without sky-subtraction; the difference should be in the "_icubes" files; is this correct?

Also, when I do sky-subtraction, the algorithm doesn't seem as simple as "icube=ocube-scube"; I get residuals of about 1 part in 10^7 (but definitely not zero). Can you please explain?

BTW, we are NOT using N&S.