Garland, slope is confusing because the number doesn't tell you how hard the course is for bogey (average) golfers). It just shows you the difference between bogey and scratch, and then throws in a multiplier to make things even less accessible.
i.e. a course with 130 slope can be harder for bogey than another course with 140 slope.
Bogey rating (which slope is partly based on) shows the average golfer exactly how hard any course is supposed to be for him. If you also know the CR, you also know exactly how much harder the course is supposed to be for bogey vs scratch.
Shel, the constant is a multiplier. It magnifies the difference between CR and BR. There is no mathematical reason for it, and no practical reason either, except to make a fairly small number look bigger. Also, they artificially cap slope at 155. Why??
As it stands, bogey golfers would do better paying attention to CR than slope, if they want to know how hard any course will likely be for them. IMO they should forget slope, and instead list CR and BR.