I read this thread last night and decided to put this theory in practice.
Originally Posted by Bruce Osgood
While I don't agree with your example(!?), I found that the formula worked fine. Well, fine enough to be a pretty good starting point (I always test strip regardless).
I also found this one elsewhere on the net. Same formula in essence:
(ot/oh^2)*nh^2=nt, (old time divided by square of old height) times square of new height equals new time.
So, thanks to this thread, I am now saving a lot more time in the darkroom!!