Richard M. Nixon once used a subtle idea from calculus in a political argument during his campaign for re-election. He claimed that the rate of increase of inflation was decreasing, a statement often described as the first time a sitting U.S. president implicitly invoked the third derivative to support a policy claim. Inflation itself measures how the purchasing power of money changes over time, so it can be viewed as a derivative. The rate at which inflation increases is therefore the derivative of inflation, which corresponds to the second derivative of purchasing power with respect to time. Saying that this rate is decreasing means its derivative is negative. In effect, Nixon’s claim implied that the second derivative of inflation, or equivalently the third derivative of purchasing power, was negative.