Why is elevation so badly off?

[ScottKilbo]

Since getting my Surge, I have done a number of walks around my neighborhood and a couple of other areas.  When doing these walks, I always walk the exact same path.  When comparing the elevation plots for these walks, they are pretty dramatically off from each other.  I have walks that have elevation gains that are more than double other walks.  I walk in a large, 4 mile circle, starting and ending at the exact same point.  I look at the elevation plot for these, and it shows me starting at a higher point than I'm ending.

The GPS seems mostly accurate, when compared with my old Garmin GPS, but the elevation is just silly bad.  Why is this the case?

[MarreFitbit]

It's nice to see you around @ScottKilbo ! I'd recommend taking a look at these threads #1 and #2 to clarify what could be happening with the elevation on your Surge. 

Happy stepping! 

[ScottKilbo]

Thanks.  Neither one of these threads seems to deal with the issue directly.  My problem isn't with floors.  It's with elevation when the GPS is on.

[MarreFitbit]

Thanks for getting back @ScottKilbo! Well, I'm not pretty sure what you're talking about since I'ven't heard that before.. The Surge does in fact use it's own GPS capabilities while in activity tracking mode. You can learn more here.

If you're doing everything correctly, but the GPS keeps showing wrong data I'd recommend getting in touch with Customer Support directly so they can do a deeper investigation and see where the issue is coming from.

TGIF, have a good one! 

[SunsetRunner]

I work on aircraft avionics which includes GPS systems. I could go into the techincal discussion about how elevation is determined, but it's long, boring and math intensive.

Or, you can just Read This Article which is short and to the point.

Basically, this is a fitness watch, not an expensive GPS receiver. Same with our smartphones. No iPhone or Android app using GPS is going to give you accurate elevation data. I use Endomondo on my Samsung S6 and the elevation data is just as inaccurate as the Fitbit.

[SunsetRunner]

In a ~1.5 inch square by ~1/2 inch thick package, Fitbit has shoe-horned a touch screen, bluetooth, GPS, HR monitoring system, barometric pressure sensors, accelerometer, and three days worth of memory (am I forgetting something? probably)... and computing power to utilize all these features. All this, and a battery that (generally) lasts 4 to 6 days.

But I get it... we want everything to work like we think it should work. And before I was employed in aircraft avionics (which includes familiarity with how GPS works, and the experts to ask should you require more info), I too demanded that my smartphone GPS be more accurate than it could ever possibly be. But, I don't think you really want the long drawn out techincal explanation (you can easily google it if you did) of how GPS works, you just want to know why your Fitbit isn't giving you what you expect.

This article, while less techincal, is pretty straight forward as to the limitations of cheaper GPS systems.

Bottom line: Smartphones and fitness trackers have to make sacrifices.

FWIW - You can map your GPS routes at (websites like) walkjogrun.net which will give you a more accurate elevation result.

[ScottKilbo]

I understand all of that, and I understand that these things are only kind of accurate.  I accepted that about consumer electronics a long time ago.  I was just wondering if it's normal for this device.

I'm not expecting miracles out of a 249 dollar gadget.  When trying to decide on a wrist based exercise gadget, I reviewed them all, and they are all plagued by inaccuracies in GPS and, particularly, heart rate.  I chose fitbit because I've been wearing a fitbit since 2010.  I figure that if it's within .1 miles of the actual distance, I'm good.  My wife and I both wear Surges when walking, and we're usually about .1 apart from one another, even though we're walking right next to one another.  Funny thing is, yesterday I wore a chest strap to get my heartrate, and the fitbit was exactly the same as the strap.

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@SunsetRunner wrote:

In a ~1.5 inch square by ~1/2 inch thick package, Fitbit has shoe-horned a touch screen, bluetooth, GPS, HR monitoring system, barometric pressure sensors, accelerometer, and three days worth of memory (am I forgetting something? probably)... and computing power to utilize all these features. All this, and a battery that (generally) lasts 4 to 6 days.

But I get it... we want everything to work like we think it should work. And before I was employed in aircraft avionics (which includes familiarity with how GPS works, and the experts to ask should you require more info), I too demanded that my smartphone GPS be more accurate than it could ever possibly be. But, I don't think you really want the long drawn out techincal explanation (you can easily google it if you did) of how GPS works, you just want to know why your Fitbit isn't giving you what you expect.

This article, while less techincal, is pretty straight forward as to the limitations of cheaper GPS systems.

Bottom line: Smartphones and fitness trackers have to make sacrifices.

FWIW - You can map your GPS routes at (websites like) walkjogrun.net which will give you a more accurate elevation result.

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[SunsetRunner]

Then I apologize for my reply, as it didn't seem from your post that you understood it at all when you said, "but the elevation is just silly bad. Why is this the case?" ... and the title of the post itself is "Why is elevation so badly off?"

[ScottKilbo]

Understood.  I suppose that I could have phrased that better.  Like, "is this normal for this device", for instance.