My husband bought this watch for me last winter. I was having what I thought were funky symptoms and thought a watch with continuous heart rate might help me. Long story short, the ""funky"" symptoms turned out to be a heart attack, and I ended up in cardiac rehab.I tell you that to make what I'm about to say understandable. This little watch is an excellent fitness tracker for casual use. It does a fine job of providing 24/7 heart rate, if you want it, or of sampling and giving you an average heart rate, if you want that. It gives lots of info about your sleep patterns, and overall activity levels. It scores your daily activity based on your overall level of activity, rather than just footsteps, which is great. It syncs over to My Fitness Pal and coordinates with your food intake if you're dieting. The optical HRM is plenty accurate enough for daily life and a casual work out. It's a great choice if you are just using it to help you get fit and feel better.If you want to wear a Polar HRM on a strap for greater accuracy, you can. It works just fine, and is ez-pz to use. I did that for quire a while, and it synced easily and worked well. That ability puts this little fitness tracker in a much higher level of ability than most of it competitors out there on the market.Buuutttttt, I ended up in cardiac rehab. And because of the nature of my heart problem, I needed an accurate heart rate tracker. This little guy tracked with the EKG in the lab quite well until I was deep in my workout and dripping with sweat. Then it reported heart rates that were consistently about 20 bpm higher than the EKG.That wouldn't be a problem for most people. First, I would never, before the heart attack, have exercised enough to sweat like that, where I was literally dripping sweat onto the equipment and had to use a towel to wipe both the treadmill and myself down. Second, even if I had, the deviation on the heart rate wouldn't have been important.But for me, with my heart condition, it really mattered. When I exercise, I need to stay below certain numbers and above others, and it matters a lot that I do it that way. I talked to the rehab people about this, and the conclusion was that NO optical heart rate monitor is accurate enough for following a cardiac rehab prescription. I opted for quire a while to use it with the Polar H7 heart rate monitor. That gave me an accurate heart rate, but the watch was still awkward to use with the phased workouts that were part of my rehab prescription.I got tired of fiddling with the watch in the middle of trying to get my heart rate to certain levels during the different phases of my workout. I ended up buying a Polar v800 with their H10 heart monitor to track my workouts.That's kind of a hoot, since I'm not the least bit athletic. But I need the ability to transition between levels of heart rate, and to different types of exercise in a timed progression, and I need the heart rate on which I'm basing my workout to be within a few beats of accurate. The v800 with the H10 tracks right along with the lab's EKG. It matches it almost beat for beat. There are a lot of good things about this, but one that's important to me is that I feel safer, knowing that I'm not pushing my heart too hard and going to get myself in trouble, or, that I'm not pushing it hard enough and failing to condition it properly.I still use my A370 for daily use. It's small, light, attractive and loaded with every option I need for that. Both watches sync to Polar Flow and the software combines the data into one seamless presentation that is fun and informative to study. It's a good combo for me. The a370 is a great watch for ordinary fitness tracking and casual exercise of the I-want-to-look-good-and-feel-better variety. It's ability to sync with a chest strap HRM when you need it gives it a much higher level of accuracy than other fitness trackers in this price range, if you need that.