Shoot any uniform surface without texture illuminated by light you normally use (ie tungsten vs daylight). Focus lens at infinity. Shoot zone I. Place processed negative over light meter, the frame that drops exposure by 1/3 stop = 0.1 log d = good exposure index.
Thank you ic-racer. Will do it that way. I still like the idea of ball-parking development time first. Then do this. And if a repeat of this process is performed, logically one would have it nailed.