Regarding Purchase Invoices Other educational accounting software (PS Financials, SIMS FMS), in accordance with audit requirements, generates a unique, sequential reference number to each document on posting. Documents are then filed in that order. When auditors come to do their sample check, the source documents they highlight from a system generated report can then easily be retrieved using that system generated number. The auditor also gains assurance from the system generated numbering system for each type of document that records are complete.