A sample sits in the optical path as another transfer stage, reducing the signal by its own fraction rather than through a Beer-Lambert absorbance law. The optical stage passes 1/2 of the source 24, then the sample transfer is 1/3, giving output 24 times 1/2 times 1/3 = 4 exactly for the stated toy transfer ledger; real samples scatter, bleach, saturate, vary spatially, and carry measurement uncertainty.
A sample stage can reduce a deterministic optical signal. 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 optics set the incoming signal
The optical stage passes 1/2 of the source.
Safter optics=24⋅21
The sample adds one more transfer
The sample transfer is 1/3, so the output is 4. This is not Beer Lambert absorbance.