A correction fraction of one half moves halfway to the target each step. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Half correction moves halfway to the target
Starting at 0 volts with target 8 volts, correction 1/2 moves to 4 volts.
0+21(8−(0))=4
The remaining error halves each step
The checked states are 0, 4, 6, 7 volts, with final error 1 volt.