Use

This graph shows the Gross Federal debt, nominal and real:

Graph #1: Federal Debt (blue) and Its Inflation Adjustments, Right (red) and Wrong (green)

Nominal (blue) is useful for figuring the payback of debt. Real (red) is useful for figuring the boost that credit use gives the economy. The third calculation (green) is wrong and should not be used. These rules apply not only to government debt, but to all debt.