jnaneshwars, contrary to Ray's comments, this is not my approach. I borrowed it, copied it, stole it, whatever you prefer but I did not invent it. It is not mine.
Michael Reichmann for one says there is no difference between film and digital when determining DoF. I happen to agree with him, but if you don't, take it up with Michael Reichmann, not me.
Now, now, Howard. Don't get uptight about this . I think most people would understand that I am not implying you have invented this system, but rather you have adopted it. I notice again you have this strong tendency to appeal to authority during differences of opinion. Ansel Adams or Michael Reichmann wrote 'such and such'. They are experienced and revered photographers, therefore they must be right.
Surely by now you must know that my view is, all knowledge is provisional
It matters not whether I can measure the focus or hyperfoacal distance or not. It might be in the middle of the Grand Canyon. I may have to estimate, or guess where to focus. But even if I can't measure the focus distance and have to estimate it on my lens, it is far better, in my opinion, to know (even precisely ?) I am trying to focus at precisely 122.3 feet, rather than simply take a flyer - try to focus at a guessed distance that I have no idea what it is, except perhaps it is between this bush and thta one.
You have just contradicted yourself in the same paragraph, Howie. If it matters not whether you can measure the hyperfocal distance, there cannot possibly be a reason to guess.
However, I agree, if it is necessary to guess, then you are better off having a precise distance to 'guess around', especially if you lack experience in such matters.
As regards choosing different CoCs in relation to intended print size, I think that's probably another unnecessary complication for most photographers, but a principle one should at least be aware of. I would recommend sticking with a CoC appropriate for the maximum print size in relation to an uninterpolated image at 240ppi.