Quote Originally Posted by Stephen Benskin View Post
1 point maybe. It's easy to key off a tone in printing. For black and white negative film, it's a little harder. The only knowable point is the tested speed point and that is influenced by flare. The density at the metered exposure point depends on the shape of the film curve.
It seems to me that if we use any given negative film, processed in a given and consistent developing regime; that a given amount of exposure, should get us a given film density at the same point on the curve every time.

I see no reason or evidence in my own experience to suggest that I should expect inconsistent results, except for flare. So it seems to me that because of flare the actual/effective speed point for any given shot in the field would actually be the least knowable point on the curve.