A candidate wavelength is evidence only when it matches the checked path. 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 stale wavelength would not close
The accepted path is still 6 metres. A stale 5 metre wavelength is not the same ledger.
5=6
The ledger keeps the accepted bit at one
The reflection check carries accepted bit 1 only for the cited spacing, path, and wavelength.