A finite voltage trace is first a checked sample ledger. 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 samples are the source ledger
The four samples are 2, 4, 6, and 8 volts, so the checked sum is 20 volts.
2+4+6+8=20
The average is tied to the count
The count is 4, so average 5 volts is not a copied label.