They're never gonna be 100% and probably nowhere near a chest strap type set up, you are moving, the watch is moving, you are sweating, all has an effect on the accuracy, they are a rough guide at best... I was on the cross trainer before and for my last minute I always go full pelt, the monitor on the machine indicated 165 pulse which for the intensity of what I was doing would be about right, the fitbit was reading 108... very disappointing really I had higher hopes, also I looked down at the watch a few times and noticed it dropping well below 110 bpm which considering I keep a constant pace up and the machine rarely read below 145 I feel due to the fitbit losing your pulse due to the things mentioned above I would imagine they always read a bit lower than what you've actually burnt, the cross trainer was reading 960 calories in an hour my watch said 776... I know the cross trainer isn't terribly accurate as it doesn't know your height so it will Base it's calorie burnt estimate on an average person and considering I'm 14.3st or well over 200lb and less than 10% body fat I probably burn significantly more than an average person so the watch must be way out I'm guessing... if you are looking for something that's on the dot data-wise these seem to be quite a way off the mark I'm afraid!
