I thought the same thing. The problem with a linear graph is that you lose sensitivity to relative change once the trace gets close to zero. My benchmark has been the price of postage stamps and the price of gasoline. When I was growing up in the 50s, a postage stamp was 5 cents (modern keyboards no longer have the cent symbol). A gallon of gasoline was 25 cents. A dollar today would have been worth a dime in my youth. This inflationary creep has the effect of driving everyone into higher income tax brackets, even though our buying power has not improved.