Reciprocal-map dots are useful only when their indices are bound. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Reciprocal spots sit on integer coordinates
The checked spots are at index pairs 1,0; 0,2; and 2,1.
(h,k)∈{(1,0),(0,2),(2,1)}
The spacing and spot map share the same check
The spacing claim remains 2 metres while the spot count is 3.