The Y-index is a measure of a golfer performance on a hole defined by

Y-index = trunc( 10 * ( score - median ) / ( best_score - median ) )

The Y-index does not make a distinction between veteran golfers and beginner golfers. The median is extracted of the whole scoreboard.

The Y-index adopts values from -10 (the best) to arbitrary large values (in case there is rogue Perl bowlers amongst us). A score of 0 means that your are in par with the course.

The Cumulative Y-index (C. Y-index) is the sum of a golfer's holes' Y-indexes.

The Normalized Y-index (N. Y-index) is the sum of a golfer's Y-indexes, divided by the number of holes played.

For those who care about such details, the median is used instead of the average to better capture the "average golfer's score", and protect us of nasty score variances.