A detector baseline should be scanned as a source factor before gain. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Dark baseline two leaves net ten
Hold measured count at 12 and gain at 1. Dark baseline 2 leaves net output 10.
12−2=10
Dark baseline four leaves net eight
Dark baseline 4 leaves net output 8. A larger baseline removes more of the same measured count.
12−4=8
Dark baseline six leaves net six
Dark baseline 6 leaves net output 6. This is a fixed-baseline correction only, not a noise distribution.