Three syndrome-round patterns separate no error, check fault, and data error. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Baseline readings choose no correction
Readings 00, 00, and 00 keep correction index negative 1.
s:00,00,00c=−1
A one-round blip is a check fault
Readings 00, 11, and 00 return to baseline, so correction index remains negative 1.
s:00,11,00c=−1
Repeated nonbaseline readings choose data correction
Readings 00, 11, and 11 repeat the nonbaseline syndrome, so correction index 1 is checked.