Neil, it is the activation of the book that builds the comprehension. The best way to bring about optimum comprehension is to use a method similar to the 5 day test on it. That way you are training the inner mind to bring the information to the conscious mind. Photoreading the book once is enough for the inner mind. If you apply the 5 day test to books that you really need to comphrehend (allowing yourself more than 5 days for complex and larger volumes) Then you will know consciously that your comprehension has improved.
Photoreading frequently the same book does improve the inward knowledge of the book but you don't know that you know or what you know until you are tested. It's a good method for language dictionaries. 
It doesn't hurt to photoread a book a few times. Just avoid worrying if you've done it often enough for activating a book. Once is enough in order to activate the book.
Alex
[This message has been edited by AlexK (edited September 09, 2002).]
