This agency grades on a scale of one to ten, with ten being the highest grade. This reflects the representation of special patterns throughout a mating. The grading assessment (which is done horse by horse individually) looks at the ancestors of the resulting foal of any mating as four separate quadrants. Each quadrant has its own special significance in the sex of the individual represented in the mating. And while one can evaluate a mating as close as these individuals, it can be carried through each generation behind it, as far as the breeder desires.
A mating showing no patterns, which is virtually a perfect outcross would receive a mating of 1 - 2. This is not necessarily a negative. However, matings that have such an appearance need to have rationale for using an outcross. Breeders need to be wise to how and when to employ an outcross and to help those planning matings for their mares, this agency makes note of low ratings that could be effective outcross matings.
Matings that are found throughout the population that show some duplications, but represent little planning and appear to follow a mantra of "breeding the best to the best" are rated "5" to represent the mean or average of the breed. Because good horses are not proven to appear from one source with regard to mating potential, you do find good runners with average matings. Such horses are the beneficiaries of "everything good" from their parents, both physical and ancestral. Such horses, while existent, do not represent a high "strike rate" from the pool of genetic material they are drawn from and thus not the optimal horses to mate unless the physical far outweighs the genetic in your mating plan.
Matings this agency gives a grade of 7.5 and higher are individuals who have proven patterns striking in 75 percentile of their ancestry and higher, that is, they strike on three of four quadrants of their pedigree. This gives a breeder a far higher likelihood of having the genetic information from the best individuals passed down in some form. This is by no means a guarantee, but it has become the experience of this agency that horses bred with these types of matings and patterns win more often, and perform in stake company with greater probability than the population of horses bred in an average way.
Patterns are unique to each individual horse and are rarely duplicated. Even when considering the probability of the genetic code, full siblings still offer huge genetic variation. Your own siblings, unless twins, are testament to this fact. The probably of duplicating the human genetic code is said to be 84 billion to 1 and has high as 43 trillion to 1. Perhaps considering this fact makes all the pedigree discussion completely pointless, yet the consistencies in equine pedigrees are compelling and the successes of those who dedicate their lives to solving the puzzle are good evidence for one to try to follow the clues.