Structural welding code preheat zones (zones 1/2/3)

Believe me, if you don't have someone to take you through this the first time, it's a mess. The first time I ever looked at this, it took me about two hours to figure out what they were saying, and I had some background. Here's the carbon content and here's the carbon equivalent. I'm going to plot the two, and I can be in zone one, I can be in zone two, or I can be in zone three. Zone one is carbon steel — easy to weld, tolerates 30 ppm hydrogen, all kinds of things. Zone two is over here, this is some of your higher-strength quenched-and-tempered steel. HY80 submarine steel is kind of right over here near this line, but it's in zone two. 4340 — oh no, this stuff is a real pain. Zone three, you're going to be getting up to these five- and six-hundred-degree Fahrenheit preheat temperatures.