What is a score differential?
After every qualifying round your score is converted into a score differential. This takes into account how difficult the course was, so a round on a tough course can be compared fairly with a round on an easy one. In the Netherlands the score differential is often called the dagresultaat (day result).
How it is calculated
The formula is: (113 / slope rating) x (adjusted gross score - course rating - PCC). The adjusted gross score is your score where you count at most a net double bogey per hole. The PCC is a correction for exceptional conditions, such as extreme weather, and is usually 0.
Example
You play a course with a course rating of 71.2 and a slope rating of 128. Your adjusted gross score is 90 and the PCC is 0. Your score differential is then (113 / 128) x (90 - 71.2) = 16.6.
From score differential to handicap
Your Handicap Index is the average of the 8 lowest score differentials from your last 20 qualifying rounds. If you play 9 holes, your score is supplemented with an expected score for the other 9 holes, so you still get an 18-hole score differential.
