I found it on the Leupold Answer Guide:
What is Boone & Crockett Club Big Game Ballistic System?
Leupold Ballistic Aiming System: Boone and Crockett Club Big Game Reticle This aiming system provides a series of additional aiming points to improve your ability to shoot accurately at longer ranges. Taking advantage of the long appreciated method of establishing a sight in point that extends the effective point blank range, that range at which the drop of the bullet is effectively insignificant, the first aiming point is designed to be used at 200 yards with most common big game cartridges. In addition, a large and a small triangle indicate two power selector positions that are provided to allow the shooter to select the subtensions to best suit the cartridge they are using. With this system, the marks always represent the elevation needed at easy to remember, rounded to 50 or 100 yard increment ranges with simple setup and no reading of charts or calculations in the field needed Aiming points on this reticle are patterned after Leupold’s unique CPC reticle, with tapered marks that draw the eye to each 100 yard increment aiming center as that aiming point is used. The thicker end of each CPC mark indicates a common 10 mph wind drift point. The VX III ranging system is also available with this reticle. A game animal with a brisket height of 16 inches can be bracketed between the center aiming point and the top picket. Turn the power selector ring until the brisket just fills this bracket, then read the range on the power selector ring. For best performance, get intimately familiar with the ballistic performance of your rifle; however, a simple rule of thumb will get you close. The 21 Inch Rule applies for determining how to set your power selector. If, when sighted in at 200 yards your bullet drops 13 to 21 inches at 400 yards, set the power selector on the big triangle. If it drops more than 21 inches, up to 28 inches at 400 yards, use the smaller triangle. With this the error will be no more than 4 inches at 400 yards, 8 inches at 500. For cartridges flatter shooting than the 13 inch drop at 400 yards sight in at 300 yards and use the big triangle. The aiming points now would correspond with 300, 400, 500, 550 and 600 yards.
[ 01-28-2004: Message edited by: thequickad ]