Eight features (four for the forward strand and four for the reverse complement strand) are associated with every queried site. Each feature consists of a 25-base oligonucleotide. The 13th base is the query base and all possible genotypes are tested. Each feature is divided into 56 equal pixels, and the pixels are scanned individually. The outermost 26 pixels are “masked,” so that only the 30 interior pixels are used for any calculation.