Every earlier reflection ledger in this book fixed diffraction order at one and scanned the Miller family; this scan holds spacing and ray geometry fixed and scans the order itself. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Every earlier reflection row held diffraction order fixed at one
Every earlier reflection ledger in this book fixed the diffraction order at 1 and only ever varied the Miller family or the ray geometry. Here spacing stays 5 m and the ray triangle stays fixed, but order itself is 1, giving wavelength 6 m.
6/1=6m
The diffraction order itself sets the accepted wavelength
Spacing and the ray triangle never change across these rows. The diffraction order alone divides the same path difference into a different accepted wavelength.
6/2=3m
A third-order reflection accepts a third of the path difference
At order 3, the same path difference gives wavelength 2 m. Three rows separate diffraction order from the Miller-family factor already scanned in chapter six.