Just wanted to say I used the "geometric", or ISO numbers method last night and loved it. The negative I was printing was VERY difficult. Mostly over exposed, but some under exposed shadows too. I started at f11, and a base exposure of 16 (and worked up 20...etc). Found that I needed one more stop, so bumped it to f16. The 1/3 stops really helped nail down the right exposure and eased printing. I settled on 25 seconds for the main exposure, but some areas needed to be dodged. To aid in dodging/burning I knew from the scale I drew out that I could decrease the apeture to f22 and increase the time to 50s, which I felt gave me more control in being able to dodge the under exposed areas that held a lot of detail.
I'm not completely finished with the print, but this method got me to a good working print on a very difficult negative a lot faster than I normally would have!