The main graph is easy to read and operate. Our timing retards for boost is shown in the lower right corner. Along the top axis is the manifold pressure, and the axis on the right is the amount of timing removed. As you can see, the curve prescribed by Burcham starts off slowly and the timing removal gets more aggressive as boost increases. The graph on the top is turned off and is a timing retard based on engine rpm. The rpm/retard graph is useful for traction-limited applications. A user can leave the starting line with timing removed so the tires hook to the surface. As the engine climbs higher, the timing retard backs off and full timing can be had at a predetermined rpm level.