Why can't you measure the efficiency of PRing? You can setup some tests and measurement criteria. Probably not too easy too do with great certainty. Comprehension is a tough one. Unbiased and similiarly capable test subjects can be hard to come by. Placebo effect would need to be modelled too. However, I suspect it could be done. Of course you could just do some testing yourself... the problem is that you will usually see the results you expect to see; for one reason or another.
Why Photoread a text again. Well as all powerful as your mind is, it doesn't work on all problems with the same effort. Those problems that are more important or more urgent or more present in your thoughts (or other than conscious thoughts) get the greater share of effort. So if you PRed something and haven't needed or use the information, but two years later you think you do. Well your mind probably didn't carry the book around for two years, just incase. However, maybe it incorporated some Important lessons into your being without you're noticing. So PR again if you feel you should. Trust yourself to make the right choice. Or play cautious and throw a few minutes into PRing again.
What criteria? Do you feel you should or need to do more passes.
Should I concentrate more on PR step? Think about your purpose, your desired results, and just do the PR step.
I PRed last week, do I have to PR again? I don't know. Do you?
Maximum time between PR and activation? One life time. Sorry, I couldn't resist.
Multiple activation passes and it takes a long time, so should I PR again? Again you be the judge. If you are doing one 20 minute activation pass a week, just how motivated to learning the material are you. If you're not motivated, don't expect your mind to hold onto it.
PRing for 4 seconds. I think that is pretty long. I'd worry that you conscious mind is going to break your ALS. Longer doesn't mean stronger impression on the inner mind. 1 second is probably more than excessive.
Second post:
There should be....
Well PWMS is not a recipe book. It is a guide to help you develop a skill.
Well that's the most AlexK like post I've ever given. By that, I mean addressing each question in turn. I usually just grab something I feel is important and ramble on about that. For dantitan, it would be use the system and stop analysis it. It's less complicated than you are trying to make it. Again the guide versus recipe book comes to mind.
Keep at it,
Iam2