Whether we manage our own investment assets or choose to hire others to manage the assets on our behalf we are keen to know how well our […] portfolio of assets is performing1 and the calculation of portfolio return is the first step in [that] performance measurement process1. Now, while the matter of measuring the rate of return of [a portfolio] appears, on the surface, to be simple enough2, the presence of external cash flows - either contributions to the portfolio or withdrawals from the port