Indeed I was confusing the log of Exposure units with the density resulting from that exposure. I went back and read it again and thanks to all notes above I got it. Thank you all. I will read those books, I promise.

Now going back to what I was trying to achieve which was determine my N+1 time to move Zone VII up to VIII and my N-1 to move zone VII down to VI . my N+1 time of 30% more development is correct. , however my N-1 -30% less development time has dropped the zone two steps which means 30% less was to low, I should cut it to about -15% . Is my reasoning correct ?

thanks,