When an auditor feels as though they cannot rely upon the books and records of the taxpayer being audited, they can avail themselves of the net worth methodology. In this method, rather than auditing the actual books and records of the taxpayer, the auditor calculates the difference between the taxpayer's net worth (assets less liabilities) at the beginning of the audit period and at the end of the audit period. The auditor then adds to the change in net worth (an increase or decrease), the cost of living for the taxpayer for the period in question. The sum of these two figures will be used by the auditor to determine the taxable income for the taxpayer over the audit period. This figure is in turn compared to the figure reported by the taxpayer. While this methodology is widely used, the CRA Auditor's manual indicates that it is a method of last resort, which should only be used in limited circumstances.