I’ve been playing with the Fitbit Charge 2 for the last couple of weeks.

As I was reminded when I posted on Reddit about the experience, there’s a lawsuit against Fitbit that claims its heart rate monitor is egregiously inaccurate. But from what I’m seeing, the tracker output squares up well with actual challenges I’ve been tackling. I can’t speak for the accuracy of the exact BPMs, but the scale, timing and trajectories are all right on point. Two examples below.

Take the ten mile trail race I ran yesterday. My heart rate, as recorded by Fitbit, tracks up and down as I cruise the many hills and valleys (and divots within bumps within hills) of Little River State Park north of Durham NC. (Thank you Trailheads for putting on another awesome race!)

Throughout the race, Fitbit’s chart shows a steady increase as my heart tries to keep pushing my tiring body along. And then there’s a final surge in the last couple of miles when — my legs and judgement a little numbed and my mind a little euphoric — I started passing people and, in the last half mile, sprinted to the finish line.

Very roughly and taking out the initial quarter mile and last sprint, the chart shows an average of high 150s, with a variance of plus/minus 15 BPM. (My chip time was 1 hour 55 minutes, 5 minutes better than last year.)

Compare that hilly run and graph to the graph of my 1.5 mile run this morning along a bike-path beside a train track near my house. Like the flat path, my heart rate is remarkably steady, with a smooth cool down as I walked the final stretch. Taking out the warm-up and warm-down, Fitbit shows my heart tracking at 155 plus/minus 5 BPM, which fits well with the geography and my tempo.

Anyway, lots more exploring to do.

(See my initial thoughts on the heart rate monitor HERE. I fear the next step is buying a chest strap HRM and comparing results.)