I have the garmin edge 305. I do not believe it subtracts from the total as you descend. It gives a different total for ascents and descents. I like the garmin edge because it collects all my data (heartrate, cadance, speed, elevation, grade and more) while I'm riding. At the end of the ride I can download it to my computer. It has a program (training center) that gives you a map and a graph of your ride. You can also upload it to a site (motionbased) on the web that will let you look at your ride through satellite...which is very cool.