An audit rarely turns on arithmetic. It turns on reproducibility: can you show the same inputs producing the same figure, and can you show who changed anything in between.
Three things to be able to produce
- The rule that produced a figure, and when it last changed
- Who adjusted a payroll entry, when, and what it was before
- Evidence that a finalised period has not been edited since
If those three come out of a system rather than out of somebody’s memory, most of the preparation for an audit disappears.