Establishing purpose before PR is very important i know. I heard a photoreader said he would choose to "preview" first b4 "prepare" if he X know what the book is about.

I tried it with a chapter in my textbook. However, after preview it, i came out with too many purpose. I dun know which is my real purpose. for example in the chapter "dynamic", will hv many subtopic like Newton's law, calculations, and etc. If establishing purpose is based on WHAT I need out of this chapter, then i will say the purpose is what i need from this chapter to get an A in the exam . Then there will b no purpose for me...As in the exam, we hv to really understand a chapter to score A and not just understand things that r of my personal need. I'm studying for exam which need high level of understanding. Anyone can help me? Is the purpose should sound like "to know anything 'bout dynamic"? Or be more specific? Can i use many purposes together and PR and activate together in one round?