The beauty of this table is that we can easily compare any two years prices, not just a given year and 1982. The Table below shows the official CPI since 1982. We will explore how it is used. The interpretation of the CPI in the last paragraph allows us to compare prices in two different years. On the face of it, it seems that gas is more expensive in 1997.
Economists refer to prices from a given year as nominal or current prices.
Nominally, gas was more expensive in 1997. To compare the prices taking into account the changing value of money, we convert one of the prices to the same year as the other. Usually, we convert forward to the more recent year, but one could also convert back to the earlier year. So gasoline was significantly cheaper in 1997 than it was in 1990. Economists say that the equivalent price in a different year is in real or constant dollars .