This natural base is called e. It’s a number close to 2.718 (I’ll explain where it comes from in a minute), but its numerical value is beside the point. The important point about e is that an exponential function with this base grows at a rate precisely equal to the function itself. Let me say that again. The rate of growth of ex is ex itself. This marvelous property simplifies all calculations about exponential functions when they are expressed in base e. No other base enjoys this simplicity.
