Let’s say that you had three invoices to process: $20, $30 and $40.
Before processing they are added up: $90. This total is input as a control total, followed by the three invoices. If there is an error inputting them eg $20, $30 and $50 the system would flag up that the total of the three invoices input ($100) does not agree with the original control total. An investigation would then be carried out to find where the error had occurred.