KISS... You just have to know if the mark seems to be right. Pull a plug, bring the mark up to 0°, stick a wire or long screwdriver in the plug hole and use a breaker bar (not a ratchet) and turn the crank a little each way. the wire or screwdriver should not go any higher then it was on 0°. Either way you rotate it, the wire should go down into the cylinder. If it dosen't, the true 0° mark is where the highest (farthest out of the plug hole) point is reached. See ya at the meet, Ray Jones