I don't understand what this is supposed to be showing. They seem to be only adjusting by a gas-specific CPI component: "1978 Gas Price x (2020 CPI for Gas / 19

I don't understand what this is supposed to be showing. They seem to be only adjusting by a gas-specific CPI component: "1978 Gas Price x (2020 CPI for Gas / 1978 CPI for Gas) = Adjusted Gas Price in 2020 Dollars". Which seems like a tautology... The "X Year Gas Price" and "X Year CPI for Gas" seem so linked - if you adjust this number by a number that's supposed to reflect it's rate of change, you get a flat line, but... of course? For instance, the spike between 2003 and 2006 certainly didn't feel like a flat line compared to the cost of other things, so wouldn't this graph be much more interesting if it was based on "CPI for everything BUT gas"?