Take care with the setup, and make sure your doing all things right, target, sturdy surface, do not move the cam, keep it around 10 ev, no less and not a lot more.
I used Focal for the 24-70 II yesterday and it's the first time it has been way off! It said -5 at 70mm and +5 at 24mm, but it's clearly best at "0" at all focals. I've adjusted a lot of lenses and Focal has always been right, so I'm doing a retest today.
On a happy sidenote this copy is both sharper and more accurate AF (2012) than the 2013 copy.