None

What course difficulty means. How much slower times run here than on a typical cross country course: +4% is about 40 seconds on a 16-minute 5K, 0% is typical, and a negative number is a fast course. Ratings already account for it, so a 133 run here and a 133 run anywhere else are the same performance.

What a rating means. 100 is the average runner in the athlete's pool; a rating of 133 means 33% faster than that average runner. Ratings are distance-normalised and course-adjusted, so a hard course and a fast track land on one number. Each pool (high school boys, college women, middle school…) has its own average, and the HS-equivalent view puts every pool on the high-school scale.