It takes at least five generations to reach British Guernsey. This ladder describes the fastest way:
IR--Identification Register Standard-sized female with erect ears (0%)
SR--Supplementary Register Female with a Golden or British Guernsey sire (50%)
FB--Foundation Book Female out of an SR doe with a Golden or British Guernsey Sire (75%)
HB1--Herd Book 1 Female out of an FB doe with a Golden or British Guernsey Sire (87.5%)
HB2--Herd Book 2 Male or female out of an HB1 doe with a Golden or British Guernsey Sire (93.75%)
BG--British Guernsey Male or female out of an HB2 doe with a Golden or British Guernsey Sire (96.875%)