When the test is over, Bill signs the chart to confirm the time. You leave the room to score the results. Bill sits and stews. Higher response to the control means truth. Higher response to the relevant means lying.
Equal response is inconclusive.
You apply judgement to interpret the responses on the chart paper. Using one of several numerical techniques to score question pairs, you get a total score. Bill's total is not high enough to indicate lying, because on most pairs his responses are flat. But on some pairs his responses strongly indicate lying. You judge that Bill stole the deposit.