A computed net value is blocked when its control gate fails. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Sample arithmetic can close
The sample arithmetic gives net signal 12.
18=6+12
The failed control blocks the result
The control is 8, which is outside the accepted window around 10.
10=8+2,2>1
A failed gate blocks acceptance
The accepted flag is false even though the sample net was computed.