Enter the Slope System. The number represents each golfer's playing ability on a 113-slope golf course, which was chosen arbitrarily as the course of standard ability. Since golfers play courses of widely varying difficulties, the Slope System converts the differentials into a number that assumes all scores were shot on a 113-slope course. Although it sounds confusing, it's really quite simple once you get around the decimals. Basically, it allows you to adjust your handicap each time you play a new course.
Conversion is easy.
You don't even have to do the math. Each time you go to a course with a slope rating, convert your index into a course handicap by checking the chart at the course. There will be a different chart for each set of tees, such as championship, regular and women's. The NCGA and SCGA computers automatically convert all differentials into indexes and distribute them to clubs in the same manner that used to occur with monthly handicaps. The lowest index is still shown on monthly handicap reports and still can be used for tournaments.