There is a Monthly Turnover graph on the Reporting -> Sales. It says 'September 21306.7' . I don't understand where this number is came from. On the Accounting -> Customer Invoice I have 8 invoices with

Balance: 22120 Total: 27345

which actually means that 5225 already paid. Can someone explain me why the graph says 21306.7? The same number I can see at Reporting ->Accounting -> Invoices Analysis. I intentionally turned off all the taxes and set those to 0% where possible just to figure our how this number gets calculated.