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From Fellrnr.com, Running tips
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{{DISPLAYTITLE:GPS Accuracy of Garmin, Polar, and other Running Watches}}<div style="float:right;">__TOC__</div>
I evaluated the real-world accuracy of GPS watches while running over 12,000 miles/19,000Km and recording over 50,000 data points as part of my evaluation of the [[Best Running Watch]]es. Under good conditions most of the watches are remarkably good, but when things get a little tough the differences become more apparent. However, '''none of the watches have GPS accuracy that is good enough to be used for displaying your current pace'''. For current paceAs a result, I've added the only viable option is to use a test results for various [[Footpod]]s as they can be far more accurate than GPS, and my [[Best Running Watch| review of running watches]] lists those that but more importantly they tend to have far less moment-to-moment variation so they can give a far better display of your current pace from a Footpod while still using GPS for your course. (Note that my accuracy is tests focus on the ability to measure distance, not the moment in time position, though the two are obviously related.)
[[File:GPS Accuracy.png|none|thumb|800px|An infographic of the accuracy of the GPS running watches. The top right corner represents the most accurate watches. (This graphic uses ISO 5725 terminology.)]]
The table below is a simplified summary of the results, where a '10' would be a perfect device. (For an explanation of the ISO 5725 terms 'trueness', 'precision' and 'accuracy', see below.)
|[[File:GPS Sampling Straight.jpg|none|thumb|x300px|On the straight sections, the one minute sampling does not lose any accuracy.]]
|[[File:GPS Sampling Comparison.jpg|none|thumb|x300px|Here's a comparison of 1 minute sampling (red) with 1 second sampling (blue). On my GPS testing course the 1 minute sampling lost nearly 2 miles over a 16 mile run.]]
|}
=GPS Accuracy and Recording Rate (Smart/1-Second)=
While the GPS sampling rate mentioned above has a huge impact on GPS accuracy, the same isn't true for recording rate. These two ideas seem to get confused. GPS sampling rate allows a watch to turn off the GPS receiver for short periods to conserve battery life while sacrificing GPS accuracy. Some Garmin watches can be configured to either record every second, or only record when something happens, such a change in heart rate or change in direction, something they call "smart recording." With a smart recording in normal GPS mode, the GPS system is continually active, so there's no loss in accuracy. To verify this, I tested the [[Garmin Fenix 5X]] in both the smart recording mode I normally use, and one second recording mode for comparison. As you can see, the two modes are virtually identical, and the differences are most likely due to chance (p=0.72).
{| class="wikitable sortable"
!Device
!Accuracy
!Trueness
!Precision
!Repeatability
|-
|Fenix 5X 4.30 Smart Recording
|style="background-color: #FEC97E;"|5.6
|style="background-color: #EDE683;"|6.9
|style="background-color: #FCA377;"|4.5
|style="background-color: #F3E783;"|6.8
|-
|Fenix 5X 4.30 One Second Recording
|style="background-color: #FDBF7C;"|5.3
|style="background-color: #E5E382;"|7.1
|style="background-color: #FB9073;"|4.0
|style="background-color: #FBE983;"|6.6
|}
=Device Specific Notes=
