The portable differential
Every posted round becomes a differential: (adjusted score − rating) × 113 ÷ slope — a course-neutral performance unit. Shoot 95 on a hard track and 92 on an easy one, and the differentials might match: the system compares you to the COURSE, not to par. This single idea makes handicaps portable across the planet.
The best-8-of-20 average
The index averages your best 8 differentials of the last 20 — peak-form measurement that forgives blow-ups (via the net-double-bogey cap) and ignores slumps. The 0.96 "bonus for excellence" multiplier adds a final slight polish. The design intent: the index should describe what you can accomplish, and it does.
The honesty loop
The system only works on posted honesty — and it rewards it: bad rounds barely dent the index (capped, and only the best 8 count), while skipped posting skews the record. Players who post everything get the most accurate mirror in sports; the "I do not post bad rounds" golfer is gambling against their own data.