Marc, This is too complicated to answer in a short post.Try reading Ansel Adams "The Negative" to get an overview. You can also go here: http://photography.cicada.com for a quick lesson or two. Most Zone System books recommend using a densitometer to establish film speed and Zone VIII density (or at least getting someone with a densitometer to read your negs for you). However, you can calibrate without one. See "The Zone System Manual" by Minor White, Richard Zakia et al. This is the way I've done my calibrations for years now. Good luck, ;^D)(posted 9083 days ago)