Whatever is done by the auditor in the way of checking or auditing the program, he is not quite certain that in fact only the program which he certified is used, neither is he quite sure that the operator has not suppressed or added some instructions or biased some of the input data, unless a safe-guarded automatic logbook is kept by the computer and made available only to the auditor.
Checking the program and using the processed information for auditing will thus generally not give the auditor full confidence in the unbiased operation of the system.