BTW, once you get your Garmin 500 working with your HR strap, you'll find that this unit has one of the most conservative (and probably the most correct) algorithms out there for estimating calories expended during a ride. If you're used to absurd numbers like 1,000 calories per hour, get ready for a surprise. My last ride was 74 miles, and showed 2750 calories, or around 37 calories a mile. This was on a ride where my average heart rate was at 79% of my max, with 3,000 feet of climbing and slightly over 16mph avg. I always crack up when I see people going 11 mph for an hour on a flat road, thinking they just burned 600 calories.
And for the purists out there, yes I do realize that calories based on HR is just an approximation, and that a power meter would give you an even better idea.