= Fringe-count convention inside a diffraction envelope
The ratio of an envelope width to a fringe period counts spatial intervals. It need not equal the number of bright fringe centres strictly inside the envelope's zeros. For a symmetric overlap from <phase> index $-25$ to $25$, the width spans 50 periods, but the strictly interior integer centres are $-24$ through $24$, totaling 49. Endpoints where one aperture <amplitude> vanishes have no two-beam contrast. State the count convention rather than treating these as inconsistent answers.
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