I've had my charge 6 for awhile now, after having several older versions of the charge. With those older versions, my screen would occasionally show my HR as "--" , or something similar, to say that it can't find my HR. That's fair, I'm active, and my watch does get jostled, so it makes sense that the device can't always get a reading. But with my Charge 6, I've never gotten a blank reading, except when I first put it on. What I have gotten is the occasional wildly incorrect readings-- 80 BPM a mile into a run, 60 to 150 back to 60 BPM sitting on the couch, etc. Most often, though, if I'm doing moderate exercise, it'll read somewhat low-- 20 or 30 BPM low-- until I adjust it in some way, then it will bump up to what it should be. I've proven this a few times by taking my pulse manually, as well as using other devices to check it against. I can't think of any explanation for this behavior, other than that if it doesn't know, it just makes something up.
