Net present value (NPV) is the universally accepted tool for measuring the value of a mining venture. We spend a lot of effort maximizing the NPV by changing all sorts of parameters. Essentially, NPV just converts future cash flows back into today’s dollars by compounding the discount rate ( think interest rate ) into the future. NPV discounts early cash flow less and later cash flow more. Usually, any cash flows that are more than 15 years away are attributed negligible value in today’s dollars.