The Garmin calculation of playing handicap using index/slope is wrong. This issue has been raised a number of times across these forums for over 1 year and still has not been answered or fixed by Garmin.
At my local course, my playing handicap should be 14 but Garmin calculates it as 15. I am almost certain that this is because Garmin ONLY considers the Slope of the course but ignores the Course Rating. It's very frustrating that I need to manually adjust my handicap every time I play (or change course) for the lack of a simple software fix.
Can Garmin please take this issue seriously and fix it.