A later above-threshold count does not replace the first crossing. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
A later above-threshold cycle is not the threshold cycle
Cycle 4 has count 48, but it is not the first crossing.
48≥24
The check pins the first crossing at cycle three
The accepted threshold cycle remains 3 because cycle two is still below threshold.