The last sentence is crucial: Gordon cuts off IR #3 circa 2005 – that is, 45 years from its onset, but less than half the time allowed for IR #1 and IR #2 to run their respective courses. To take a salient example from the prior industrial revolutions, this is as if the impact of the railroads on the US economy were to be measured as of 1873, 45 years after construction began on America’s first line, the Baltimore & Ohio.