You'd think that something that has been around for over 70 years would have been better defined by now. In sensitometry, 0.30 is always a stop. With Zones, I see it as a change from one Zone to the next with the original subject is one stop. There has to be a unit of measurement or else it's just gibberish. With the print, I've always thought there was too much of a coincidence between the 10 steps of the Zone System and the 10 steps of Munsell's scale. As the Munsell scale is psychophysically based, the spacing between the steps are visually equal, but not equal in reflection density. However, as the average subject luminance range is 2.2 logs and the RD range for glossy paper is around 2.2, there can be (excluding specular reflections) a one to one tonal relationship with the original subject. That is except then the print would appear dark to the view under normal viewing conditions.
Originally Posted by Kirk Keyes