As Congress debates whether or not to raise the federal minimum wage to $10.10 from its current level of $7.25, here’s a look back at when and how often the rate has been raised in the past since it was first instituted over 75 years ago during the Great Depression.

In all, there have been 22 increases, under 12 presidents and at irregular intervals. Since the minimum wage is not pegged to the rate of inflation, the purchasing power of the minimum has lagged behind the rising costs for goods and services over time. What was more or less a living wage one year might be inadequate just a few years later.

The evidence suggests that the latest proposal to raise the minimum wage would help those earning minimum wage attain a level of income not seen in the U.S. since the late 1960s.

Animation by Vince Rose.