Raw detector hits split into seen hits that pass readout and masked hits that are filtered out, and the split must close back to the raw total. The 6 raw hits equal 4 seen plus 2 masked exactly for the stated finite count ledger; real detectors add dead or noisy channels, threshold drift, pileup ambiguity, clustering choices, alignment error, readout inefficiency, and finite-count uncertainty.
Raw hits close as seen plus masked hits. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Raw hits split into seen and masked hits
The raw hit count is 6. The detector sees 4 and masks 2.