http://www.nikonchat.com/nikon-rifle-scopes-bdc/

What is the parallel approach on a rifle scope?
Nikon Monarch comes with a side approach and I am considering the Nikon Monarch 3-12X, 42 mm with Grid CDB and the approach side. Im not sure which side will focus?
This is a parallax adjustment. If you are truly staggering the time you have to put it in the appropriate footage to see the whole image, the parallax adjustment. I think this is very necessary in a deer rifle. I feel the same about the BDC. However, the scope you are seeing is very very good.
Nikon Pro Staff BDC Retical Rifle Scope