that's what I tried to over rule and clarify. After I had confirmed the average time for the band to catch up (about 40 seconds to a minute) I would assumed it would be the same if I stayed consistent with an elevated heart rate, not resting. so during a run, about 3 miles in total at the park, never once did my HR levels reach as high as the chest strap. high 170's. the only way I could confirm accuracy was cross checking with other devices (another band, my Note 4 Optical sensor, and, physically counting my pulse) after doing so, the Fitbit products were spot on. but again, thats after about 30 seconds again, counting my pulse, having the smartphone read my pulse etc. Lastly, in the past, I had tested the Jabra Sport Pulse and never had my HR levels go as high as the 170's. In general and from within my methods of testing. that's what I came up with. I hope that helps somehow or provides a but more insight how I came up with my determination.