Changes

I evaluated the real world accuracy of GPS watches using the {{Garmin 310XT}} and the {{Garmin 910XT}} while running over 1,100 500 miles/12,800Km and recording over 47,000 data points. On average, Under good conditions the watches were are all remarkably good, but this is because when things get a little tough the errors even outdifferences become more apparent.

Simply taking a GPS watch on a single run does not provide sufficient data to reasonably evaluate its accuracy. So to gather the data for this test I marked my usual running route at quarter-mile intervals, using a [http://www.jonescounter.com/ Jones counter] to provide an accurate measure of distance. The Jones counter is the device used to certify courses, and I followed the [http://www.usatf.org/Products-/-Services/Course-Certifications/USATF-Certified-Courses/Certify-Your-Course.aspx USATF course certification process]. The course I run along is a little challenging for GPS, with lots of twists, tree cover, power lines, and one bridge that I go under. The bridge carries a 4 lane road, so it's wide enough to cause the watches to briefly loose GPS signal. However, I believe that it's reasonably representative of real-world conditions, and probably less challenging than running in the city with skyscrapers. At both ends of the course there is a turnaround, and I set the mark an eighth of a mile from the end. That way I can evaluate how well the watches handle an about turn. So far I have recorded 4,658 GPS points, 3,881 using a {{Garmin 310XT}} and 777 using a {{Garmin 910XT}}. This represents 1,164 miles/1,874 Km of running.

I've divided the laps into those that go under the bridge, those that are immediately after a lap that goes under the bridge, those that go next to or under the power lines, those that turn around and then all the remainder rest (normal).

! TypeDevice! Condition

! Trueness(Average)

! 95% within +/-! Dropouts

| {{Polar RC3 GPS}}| rowspan="5"| Normal| 3,452897| style="background-color: #9DCE7E;"|0.19994%(33.1 Ft/Mile 6.3 m/Km)| 3style="background-color: #FFEB84;"|0.037 (195.01%| 126 Ft/Mile 37.0%m/Km)| 0.074 (391.2 Ft/Mile 74.1.8%m/Km)

| Under Bridge{{Garmin 310XT}} with [[Footpod]]| 2522453| style="background-color: #63BE7B;"|1.27000%(1.9 Ft/Mile 0.4 m/Km)| 3style="background-color: #C0D980;"|0.51%| 14031 (163.0%Ft/Mile 30.9 m/Km)| 1000.062 (326.0%Ft/Mile 61.8 m/Km)

| After Bridge{{Garmin 310XT}} no [[Footpod]]| 448594| 2style="background-color: #82C77C;"|0.24996%| (18.8 Ft/Mile 3.18%6 m/Km)| 12style="background-color: #FFDC81;"|0.7%042 (221.9 Ft/Mile 42.0 m/Km)| 10.084 (443.8%Ft/Mile 84.1 m/Km)

| {{Garmin 910XT}} with [[Footpod]]| 481| style="background-color: #9ECF7E;"|0.994% (33.7 Ft/Mile 6.4 m/Km)| style="background-color: #9ECF7E;"|0.027 (145.1 Ft/Mile 27.5 m/Km)| 0.055 (290.2 Ft/Mile 55.0 m/Km)|-| '''All'''| '''4425'''| style="background-color: #76C37C;"|'''0.998% (12.4 Ft/Mile 2.3 m/Km)'''| style="background-color: #DEE182;"|'''0.034 (178.4 Ft/Mile 33.8 m/Km)'''| '''0.068 (356.7 Ft/Mile 67.6 m/Km)'''|-| {{Polar RC3 GPS}}| rowspan="5"| Under Bridge| 85| style="background-color: #FA8771;"|0.952% (252.8 Ft/Mile 47.9 m/Km)| style="background-color: #F96A6C;"|0.078 (411.0 Ft/Mile 77.8 m/Km)| 0.156 (821.9 Ft/Mile 155.7 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 212| style="background-color: #F8E983;"|0.985% (81.0 Ft/Mile 15.3 m/Km)| style="background-color: #EDE683;"|0.035 (186.7 Ft/Mile 35.4 m/Km)| 0.071 (373.3 Ft/Mile 70.7 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 58| style="background-color: #FFE483;"|1.018% (96.8 Ft/Mile 18.3 m/Km)| style="background-color: #FECB7E;"|0.047 (250.3 Ft/Mile 47.4 m/Km)| 0.095 (500.5 Ft/Mile 94.8 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 42| style="background-color: #6FC17B;"|0.998% (8.4 Ft/Mile 1.6 m/Km)| style="background-color: #C4DA80;"|0.031 (164.8 Ft/Mile 31.2 m/Km)| 0.062 (329.7 Ft/Mile 62.4 m/Km)|-| '''All'''| '''397'''| style="background-color: #FFEB84;"|'''0.984% (84.7 Ft/Mile 16.0 m/Km)'''| style="background-color: #FDB87B;"|'''0.053 (281.5 Ft/Mile 53.3 m/Km)'''| '''0.107 (563.0 Ft/Mile 106.6 m/Km)'''|-| {{Polar RC3 GPS}}| rowspan="5"| Post Bridge| 166| style="background-color: #FB9474;"|0.956% (231.2 Ft/Mile 43.8 m/Km)| style="background-color: #FB8F73;"|0.066 (348.8 Ft/Mile 66.1 m/Km)| 0.132 (697.6 Ft/Mile 132.1 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 365| style="background-color: #FFDE82;"|0.980% (107.0 Ft/Mile 20.3 m/Km)| style="background-color: #D2DE81;"|0.033 (172.0 Ft/Mile 32.6 m/Km)| 0.065 (344.0 Ft/Mile 65.2 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 110| style="background-color: #FEC87E;"|0.973% (144.3 Ft/Mile 27.3 m/Km)| style="background-color: #FFE984;"|0.038 (199.3 Ft/Mile 37.7 m/Km)| 0.075 (398.6 Ft/Mile 75.5 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 86| style="background-color: #FDBB7B;"|0.969% (166.3 Ft/Mile 31.5 m/Km)| style="background-color: #8AC97D;"|0.026 (134.7 Ft/Mile 25.5 m/Km)| 0.051 (269.4 Ft/Mile 51.0 m/Km)|-| '''All'''| '''727'''| style="background-color: #FDC67D;"|'''0.972% (148.1 Ft/Mile 28.0 m/Km)'''| style="background-color: #FED680;"|'''0.044 (231.0 Ft/Mile 43.7 m/Km)'''| '''0.087 (462.0 Ft/Mile 87.5 m/Km)'''|-| {{Polar RC3 GPS}}| rowspan="5"| Turn Around| 21792| style="background-color: #F8696B;"|0.943% (301.9 Ft/Mile 57.2 m/Km)| style="background-color: #F8696B;"|0.078 (411.1 Ft/Mile 77.9 m/Km)| 0.156 (822.2 Ft/Mile 155.7 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 244| style="background-color: #FCA677;"|0.962% (200.2 Ft/Mile 37.9 m/Km)| style="background-color: #FFE383;"|0.040 (209.8 Ft/Mile 39.7 m/Km)| 0.079 (419.7 Ft/Mile 79.5 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 64| style="background-color: #FCB079;"|0.965% (184.7 Ft/Mile 35.0 m/Km)| style="background-color: #F9736D;"|0.075 (395.2 Ft/Mile 74.9 m/Km)| 0.150 (790.5 Ft/Mile 149.7 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 48| style="background-color: #FA8972;"|0.953% (249.8 Ft/Mile 47.3 m/Km)| style="background-color: #87C87D;"|0.025 (132.8 Ft/Mile 25.2 m/Km)| 0.050 (265.7 Ft/Mile 50.3 m/Km)|-| '''All'''| '''448'''| style="background-color: #FB9674;"|'''0.957% (228.2 Ft/Mile 43.2 m/Km)'''| style="background-color: #FCAA78;"|'''0.058 (304.1 Ft/Mile 57.6 m/Km)'''| '''0.115 (608.1 Ft/Mile 115.2 m/Km)'''|-| {{Polar RC3 GPS}}| rowspan="5"| Power Line| 167| style="background-color: #DCE182;"|0.987% (66.4Ft/Mile 12.6 m/Km)| style="background-color: #F2E783;"|0.036 (188.8 Ft/Mile 35.8 m/Km)| 0.072 (377.5 Ft/Mile 71.5 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 457| style="background-color: #96CC7D;"|0.01994%(29.5 Ft/Mile 5.6 m/Km)| style="background-color: #A7D17E;"|0.028 (149.5 Ft/Mile 28.3m/Km)| 0.057 (299.1 Ft/Mile 56.6 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 115| style="background-color: #D2DE81;"|0.76988%(60.9 Ft/Mile 11.5 m/Km)| style="background-color: #FFE483;"|0.039 (207.4 Ft/Mile 39.3 m/Km)| 0.079 (414.7 Ft/Mile 78.5 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 90| style="background-color: #FCEA83;"|0.984% (83.5 Ft/Mile 15.8 m/Km)| style="background-color: #63BE7B;"|0.022 (113.8 Ft/Mile 21.6 m/Km)| 0.043 (227.6 Ft/Mile 43.1 m/Km)|-| '''All'''| '''829'''| style="background-color: #B8D67F;"|'''0.991%(47.2 Ft/Mile 8.9 m/Km)'''| style="background-color: #C5DA80;"|'''0.031 (165.2Ft/Mile 31.3%m/Km)'''| '''0.063 (330.5 Ft/Mile 62.6 m/Km''')

* Away from Under normal conditions the bridge and the turnaround, the average distance recorded (trueness) GPS accuracy is quite goodfor all devices, averaging out to 0.19%, which is 30"though the 310XT/74cm per quarter mile910XT with a Footpod have a slight advantage. * Not surprisingly, the trueness accuracy drops going under the bridge and is 1.27% (201"/500cm). More interestingly, the trueness just after the breach bridge is even lower at 2.24% (355"/885cm). This suggests , suggesting that the GPS watches are struggling to reacquire the satellites.* The turnarounds are even less true accurate than going under a bridge, resulting in an average distance that is out by 4.01% (635"/1,582cm)but Power Lines do not seem to impact accuracy noticeably.* The precision [[Footpod]] improves the accuracy of the GPS watches is 3-4%310XT and the 910XT, which means that 95% of samples will fall within 12-15% of especially on the turn around and under the correct distance. For normal laps, that is 95% of laps are within 159'/4.8m per quarter milebridge.* As expectedWithout the Footpod, the GPS watches have dropouts (use satellite signal) 310XT has similar problems to the RC3 on every lap that goes the turn around, but the RC3 does worse under the bridge. The watches also have dropouts 1.8% of the time on normal laps.

** I am in the process of evaluating the [http://www.amazon.com/Polar-Heart-Rate-Monitor-Black/dp/B00BV81U7W Polar RC3 GPS], but I don't think it will make my recommendation for [[Best Running Watch]es. It may however provide a useful example of poor quality GPS reception, and as I've seen some rather erratic tracks (note to self, check Oct 10 run). ** I will evaluate the [http://www.amazon.com/Garmin-010-01128-30-Forerunner-620-Bundle/dp/B00FBYYC90 Garmin 620] when it becomes available as it has some promising looking functionality.** I am gathering data on an older Garmin 205. It's not a watch I'd recommend, but it will be interesting to see if the technology has improved over time. ** I will soon start gathering data on an iPhone 4S to see how it compares with dedicated devices.

* Look at how accurate the GPS watches are for measuring innovationelevation, and compare with barometric data.

* Evaluate how a [[Footpod]] influences accuracy. Most of my runs are with a Footpod, and this may improve the accuracy if GPS is lost.* Write up general GPS accuracy and talk about WAAS.* Check if the power lines have any impact of accuracy.