An alternating bin tests whether the samples line up with a flip-sign basis, using products before the final sum. The match is exact only for the stated sample row and finite basis vector; measured signals need timing alignment, bandwidth limits, sign convention checks, and noise/error bars.
The alternating basis is checked by products and a sum. 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 alternating basis matches the flips
The samples and basis both alternate, so every product is 1 and the dot sum is 4.
1+1+1+1=4
A shape label is not enough
The label alternating is accepted only because the displayed products add to 4.