The measuring ruler is at an angle. Done so that the aiming point on the ruler should be in the sharpest focus.
Your right, I had just started and as you can see my focus is BF. By the time I got the focus sharp on the 18" mark on the ruler the bird was long gone. I like using a light colored background as it makes it so much easier to see the two alignment holes from 70'. I should have sent an after shot too.
I am almost afraid to ask what that gizmo is ... or does?
Makes a slide rule look simple.
That my friend is a "LensAlign" system that is used to Fine Tune/Micro Adjust your sensor to the lens. I've added an aluminum yard stick so I can do the alignment from 70' on a 600mm lens. I have it attached to a tripod for easy movement. You focus on the target on the left and then look at where the sharpest point on the 36" ruler is. As it was photographed it shows a BF (back focus) condition. You know that it is properly aligned and set up to test when you can see that the focus holes line up, I'd never be without one of these.