The Purely Internal Rate of Return (PIRR) is a new way to measure the profitability of investments without relying on market rates. It looks at the ratio of net cash flow to capital invested, making it a reliable tool for decision-making and project ranking. PIRR considers the comprehensive cost of capital, which includes the interest foregone on both the capital used and the capital given up. This approach helps break down project NPV into different components, providing a clearer picture of investment returns. PIRR is more straightforward and independent of market rates compared to traditional Internal Rate of Return (IRR).