A wrong finite reference can cancel the same signal. 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 wrong reference cancels the products
With reference 1, 1, -1, -1, the products are 1, -1, -1, 1.
1+−1+−1+1=0
Zero correlation is rejected
Correlation 0 gives accepted bit 0 for this finite gate.