Breechplug is right about adjusting the power and the marks moving farther and closer apart with power setting changes, here a snipit from a article that explains it better---

The one thing that people using BDC scopes typically have problems with is that a BDC scope has the reticle in the second focal plane of the scope. If the reticle was in the first focal plane of the scope the reticle would look smaller on low powers like 3x and grow proportionately larger as the power increased to say 9x top power. The problem is that while the marks on the BDC reticle correspond accurately to the bullet drop at the know distances 200, 300yds etc. What happens when you lower the power from the scopes maximum power to any other lower power is the reticle stays the same size and the field of view within the scope increases which means that the distance between these marks on the BDC reticle no longer corresponds to the point where the bullet will strike. In short BDC reticles only work at the maximum power of the scope or at a set specific power. At all other powers these BDC reticles do not accurately represent where the bullet will strike.



Heres the link to the article
http://www.ehow.com/how_4534639_bdc-...g-reticle.html



I talked to guys at Leupold and Nikon while having both the U-Slam and Omega on the Triumph, and the scopes are designed excatly the same way. People make it way harder than it has to be to set it up and work with ANY LOAD COMBO your shooting.