The Phillips curve, in its first iteration, described the relationship between inflation and unemployment. This relationship held true until the 1970s, where it broke down. It was reborn as a relationship between changes in inflation compared to unemployment. Initially, the Phillips curve showed that the inflation rate in a given time is equal to the expected rate of inflation for that time minus a function that outlined the strength of the relationship between unemployment and wages multiplied by the actual rate of unemployment at that point in time, plus the price markup level. This was an empirical generalisation for Phillips, but was also considered as a policy tradeoff (that you could choose your level of unemployment if you were prepared to accept a higher level of inflation). This relationship broke down in the 1970s, with both high unemployment and high inflation, but the Phillips curve was reborn as a relationship between the change in inflation and the change in unemployment.