I'm new to the whole heart rate stuff. I went out for my first run with it this morning (a 10 mile run) and it said i ran 60% of it in zone4. And my race predictors have me at a 5k predicted pace of 17:15. How accurate is this stuff and should I really use the information given to me? I'm a noob at this heart rate stuff so any help is appreciated and the accuracy of the info from it.