The auto advance simply delays the timing and adds it back with detected rpm, so with those systems, you set you timing at 28 to 32 degree's, and the box does the rest. Just set those so when the crank passes the 30 degree mark, it sparks the plug, and thats close enough. Some engines have a mechanical advance, so they use a different box with no auto advance function. As long as you use the correct box for you situation (auto or mech adv) you'll be fine. With mechanical adv, I like to set the timing by fully advancing the timing mechanism, and setting it to 30 degrees. Timing at idle winds up being around 2 to 5 degree's when I do it that way. Im more concerned with the full advance, and not so much what it idles at, but 2 to 5 degree's BTDC at idle is the norm.