Proper Blind Exposure with a Gray Card

panos_m wrote:

I believe that is very simple. No matter what reflectance you put in front of it (10%, 60%, 75%, 100%) it will always read it the same that is it will always suggest the exposure that will produce the same "middle gray" raw value (the same distance in stops from saturation).

What else do you need to know to make an exposure decision and place the tonal range of the scene where you want?