When I use it for boxing, the calorie burn graph seems to very closely follow the heart rate graph. But only if the tracker was in exercise mode (longpress the button).<p>As for the article about inaccuracies. Their manual clearly states that during exercises that involve a lot of forearm flexing and vigorous arm movements the tracker will be inaccurate.<p>And I am sceptical that people wouldn&#x27;t be able to tell from how they&#x27;re feeling that they are at a dangerously high heart rate. But I guess it&#x27;s possible.<p>The highest number my fitbit ever reported was about 170 (sprinting) so it&#x27;s definitely cspable of measuring high heart rates.