I use a spotmeter and read the darkest shadow which is placed on Zone IV and I read the brightest highlight to determine the contrast range and develop accordingly, for example if the contrast range is 7 stops and the highlight falls two stops above Zone VIII I reduce development by 2 stops and increase exposure by one stop to bring the highlight back to Zone VIII. The increase in exposure is to compensate for the information lost in the shadows as a result of reducing development. I don't know if John Sexton places shadows on Zone IV, I suspect he does but I do know that Bruce Barnbaum does. I understand that any blue light present causes the meter to give the wrong values particularly in the shadows hence the need to compensate by one stop. It works for me.