I should have known someone would make me look it up.
It is called a clinometer and what some will due is place an arrow tube on the side of it and look through the shaft to the target,then look at what angle they are on,then use the chart for yardage.
This is mainly in the long distance arenas for known distanceand rangefinders are still not allowed to the best of my knowledge.So the newer rangefinders that adjust for it can't be used.
I could be wrong about that though.
If I think about it,when I get to work tomorrow,I will figure a few scenarios to compare.That is where my scientific calculator is at.
This is what it looks like on my screen.Looks like if I had excell,it might print this screen.