Quote Originally Posted by mark
Thanks for the clarification. The difference plus five means that if I get an EV of say 15 in the shadow and 18 on the highlight then I have an SBR of 8 right?

In the formula for the spot meter what value do I use for N or is it left as a letter? Would it look like this:
18-15=3 so D=3
(7*(3-N))/3

I was not metering a grey card. The shadow I wanted detail in when I first noticed this was under a rock where little rocks were holding it up. I have noticed this on many occasions. the difference between the two meters is only 3 tenths of one stop. When I was playing with the meter this happened again.

Thanks for the help folks. I have found the BTZS book to be a bit complicated. It's times like these when Dyslexia sucks
Ok lets say you spot meter your shadow and get an EV value of 15, then you meter the highlight and you get an EV value of 18, that is a 3 zone spread. Under the Zone system you would want to give it a N+2 development to get the 5 zone spread for printing....so your N value in the formula would be 2.
So if you plug the numbers:

SBR=(7*(3-2))/3
SBR=2.3

If on the other hand you are taking an incident meter and your shadow is 15 and the highlight 18 then yes, the SBR would be 8.

So you see, if you are getting both the spot metering and the incident metering to give you equal readings, then there is something wrong as per your example the SBR by the formula and the SBR by incident metering do not match. Either your incident metering placement is wrong, or one of the functions of the metering is off. When you incident meter the highlights, make sure you are pointing the meter to the light source. I am getting the feeling your placement of the meter is what is the problem.

BTW, you should really ask this question at the www.btzs.org forum, Phil Davis answers these kind of questions personally, so there is nobody more qualified to help you than him.