Simple extrapolation

Here's xkcd on the dangers of extrapolation:


...and here's some extrapolation in action:

(Click on the graph to make it bigger.)

The graph (taken from the famous 1961 economics textbook by the late Nobel prize winner Paul Samuleson) projects that the real GNP of Soviet Union will have caught up to the real GNP of the United States sometime between 1984 and 1997.

(HT: Alex Tabarrok.)