Actually the way it would work is that the exposure difference required to produce the same density difference for a middle gray across all contrast grades would be standardized. So when in the Yellow/Green range, a "d-stop" would be defined as say 1/2 stop. When in the Magenta/Blue range a "d-stop" may be defined as say 1/8th stop.
Originally Posted by Nicholas Lindan
The timer would have a peculiar function in that as you altered the contrast the indicated time in "d-stops" would change, though the actual time would stay the same. So, any time I want the mid tones 'just a little lighter' I would increase the exposure by one "d-stop" and the mid tones will get 'just noticeably lighter' whether I am in the Yellow/Green area or the Magenta/Blue area. If I used regular f-stops, a one-half stop change is going to darken the image printed with Magenta/Blue way, way more than a one-half stop change in the Yellow/Green end (which would be barely noticeable).