The Bragg row cites the reciprocal address that belongs to its family. 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 reflection cites the same projected spot
The reflection ledger names spot 2,2 and spacing 5 m.
spot=2,2d=5m
The source chain rejects an equal-looking copy
A copied spot with the same numbers is not a source unless the map check is the one cited.