I read some books for a general knowledge base, but really what matters is the steel manufactures guidance. And the different metal sources do not agree with each other either. I use the manufactures or "brand" information as a starting point and let the end results tell me what to tweak. Its mostly trial and error, the books do give a starting point, thats all though. You also have to learn your HT furnace too, my current one runs little different than my last one. I make precision parts that have to fit together correctly, so maintaining the dimensions through heat treat takes some trail and error.