Three indexed pools keep source balance visible instead of hiding it behind the total. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Three different index patterns keep the same total
The totals are 24, 24, and 24 unique reads, but the per-index rows differ.
8+8+8=246+8+10=24
A wider spread still needs visible source rows
The wide row has reads 4,8,12. It still sums to 24, so the total alone cannot describe balance.
4+8+12=24
The useful scan compares rows before the total
Index A changes from 8 to 6 to 4 while the total stays 24.