A fixed average is scanned against finite sample range. 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 average can stay fixed while spread changes
The source ledger has four samples. Its average label is computed from the same checked sum and count as the range labels.
Vˉ=420=5V
Same mean does not mean same spread
All three rows sum to twenty over four samples. The mean stays five, while the range grows across the rows.