Suppose that inflation is 2%, the interest rate is 2%, and these are constant over time. If I give you $280 today, you can buy 1 Apple Watch. Alternatively, you can put the money in the bank until it doubles in roughly 70/2=35 periods. When that happens, you will be able to buy (2x, 3x, 4x) as much money and all the prices Apple Watch (es) since you have [ in the economy are (2x, 3x, 4x) higher. This is called the long-run | of money