Except a reading of 60-80bpm when the actual is 160-180bpm is completely inaccurate.  Those are opposite ends of most people HR range.  60 is close to, or actually, resting for most people.  160 is a hard aerobic effort, bordering on anaerobic, for most people.  The FitBit, if the report is accurate, is completely useless as a fitness tracking devices (WRT to heart rate).