A useful optical readout closes transfer, calibration, mapping, and schedule. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The chain starts with checked transfer
The transfer output is 12 before dark subtraction.
Stransfer=12
Detector calibration uses the transferred signal
Dark count 3 leaves net signal 9, and gain 2 gives detector output 18.
Y=2(12 minus 3)=18
The same chain closes its capture schedule
The scan has 4 fields and 3 channels, so it produces 12 captures in 20 s.