for most easy runs in moderate conditions it works fine. But of course, I don't really need a HRM to tell me that 7:30 pace is easy. It doesn't work well for workouts with big changes of pace, or workouts at all for that matter. Usually if I were to do a 3mi warmup then 5 miles tempo, then a 3mi cooldown, it would read a reliable HR for the 3mi warmup, then when I switched from easy to tempo pace it wouldn't pick up my raised HR until the 4mi mark, almost exactly on the mile usually. then while I cool down it would still read high and never drop back down.