That is what I was afraid of. With the Nikonscan, I may measure focus points varying between, say, 150 and 175 on one slide, but only 160 and 165 on another. So for the first I would bracket at focus points of 152, 159, 166 and 173. On the second on, I would just do one scan at 162. It looks like with Vuescan I wouldn't know which scenario I was dealing with.