A threshold decision turns a measured signal into a state label by applying a declared inequality rule. The one result is exact only for the stated signal, threshold, and ideal comparator; laboratory decisions need noise margins, histograms, assignment-error estimates, drift checks, and repeated calibration.
The threshold rule turns a checked signal into a finite readout result. 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 threshold rule is an inequality
A signal of 8 is greater than threshold 5, so the checked result is one.
8>5⇒∣1⟩
The readout is a declared decision rule
The diagram does not claim electron paths or detector noise. It shows a finite threshold decision with signal 8.