There are many ways to evaluate a stallion’s performance, with those measures evolving as the breeding industry has over the decades. With the North American foal crop first expanding and then shrinking, stallions’ book sizes and career trajectories changing, and purses ballooning, all figures must be interpreted with proper context and a critical eye. Now, a means of evaluating racehorse performance that has been a respected standard for the last quarter-century can be used to compare stallions as well.