GPS distance variation between devices

[TreborSemaj]

I have a Fitbit Ionic and a Polar Vantage M. I also have a Lezyne Super GPS on my cycle and I use Strava on my iPhone 7+. They all record different distances for the same cycle ride with the Fitbit Ionic being consistently lower than the others by between 1% to 3%. Why is this?

[LZeeW]

@TreborSemaj   The first thing that users need to understand is that GPS location is not pinpoint accuracy. 

• I recently read that most smartphone GPS will put you in a position in a circle with a 16 ft radius.  So you can be anywhere within a circle of about 800 sq ft and still be correct.  I don't know the accuracy of your Lezyne, but I expect it would be similar to a phone.
• Different devices might sample at different intervals.  Points that are closer together along the line should give you a more accurate line.
• Different devices might or might not make a "correction" to put you back on the road or path.  I'm pretty sure that Fitbit does not make this type of correction -- based on the number of times my map shows me off a cliff, levitating above a ravine or off a cliff.  As an example, I know my car's GPS puts me back on a road when it can.

Does this help?

[SunsetRunner]

@TreborSemaj it takes Ionic a lot longer to connect to the GPS. When cycling this is the major factor of lower distance. Also, I find Ionic losing signal lot more often than the other devices. When you start your ride wait until GPS is connected. If it's taking too long cancel tracking and start again. It may help with distance accuracy a little.