Upgraded to a series 3 yesterday from the original. Fired up "workout" this morning and went for a walk. I got to a steep hill and as soon as my heart rate started to climb, the watch completely lost the ability to track my heart rate. It actually dropped instead of going up. Never had this issue with S0, and after searching Apple Forums, it appears to be an ongoing issue. Someone in a posting suggested that the Zones app, using the same sensor, tracks accurately suggesting that the software for Workouts may be at fault. Any insights? I shouldn't have to supplement my expensive watch with a chest strap. My wife's Fitbit doesn't have this issue and costs a fraction of this.