Exactly! The only thing I don't have with percentages that you have with f-stop timing is the headache!
Originally Posted by Bill Burk
As Bob points out, the percentages and the stops are not exactly equivalent (and reciprocity failure is always a factor at longer times), however percentages are consistent and flexible and have all the advantages and none of the drawbacks of f-stop timing. I have two sequences, 20% and 30%, that I use for test strips and have simply memorized them. No programming, no math, nothing but counting seconds.
Seriously, it seems to me that so many f-stop timing schemes (and timers!) are overly-complicated for the task at hand. Percentages are easily figured and rounded, and I can just use my metronome to time with and watch my work. Plus I have the advantage that I can apply the same system to dodging and burning, which is rather difficult with f-stop timing (how do you dodge 1/3 stop anyway?).
And, when scaling a print up or down, I can find a base exposure and then use the percentages I've recorded to figure a starting point for manipulations for the new size. I say starting point because different size prints often require very different approaches to get the same "feel."