Overall I think the data is really good. HR is within a beat of my Powertap strap. Cadence should be accurate as well because it is a pickup with the magnet on the crank arm. Also if you have the candence option it picks up a wheel magnet for even more accurate speed. Where it is off is your speed at any given point of time. It uses averages so the speed you are looking at is probably from 5 seconds earlier. This averages out over the ride so that your distance and time are correct. The elevation and calories burned data is way off. The screens are very configurable so you can put any data that you want in front of you. The only thing that I really miss was something that I had on an old Cateye and that is an indicator that tells you if your current pace is above or below the current average. Overall I am happy with the product and rarely ride without it after 18 months. I even put it on my Mtn. Bike now.