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From Fellrnr.com, Running tips
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We can look at trueness by measuring the average lap length and precision by measuring the standard deviation.
=Accuracy=
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 rest (normal). I've also included a 'mixed' category that reflects all the sectionsand a category for the straightest segment. ==Accuracy by Condition then Device=={| class="wikitable"! Condition! Device! Count! Trueness (Average Distance Error)! Standard Deviation! 95% within|-| rowspan="10"|Normal| {{Garmin 10}}| 274| style="background-color: #FCB079;"|7.740% (408.7 Ft/Mile 77.4 m/Km)| style="background-color: #FB9B75;"|0.066 (350.7 Ft/Mile 66.4 m/Km)| 0.133 (701.4 Ft/Mile 132.8 m/Km)|-| {{Garmin 205}}| 779| style="background-color: #63BE7B;"|1.381% (72.9 Ft/Mile 13.8 m/Km)| style="background-color: #C9DB80;"|0.031 (165.6 Ft/Mile 31.4 m/Km)| 0.063 (331.2 Ft/Mile 62.7 m/Km)|-| {{Garmin 620}}| 944| style="background-color: #FDBC7B;"|6.913% (365.0 Ft/Mile 69.1 m/Km)| style="background-color: #FFE383;"|0.040 (213.5 Ft/Mile 40.4 m/Km)| 0.081 (427.0 Ft/Mile 80.9 m/Km)|-| iPhone 4s| 668| style="background-color: #E5E382;"|3.046% (160.8 Ft/Mile 30.5 m/Km)| style="background-color: #EBE582;"|0.035 (186.0 Ft/Mile 35.2 m/Km)| 0.070 (372.0 Ft/Mile 70.5 m/Km)|-| {{Polar RC3 GPS}}| 983| style="background-color: #6DC07B;"|1.511% (79.8 Ft/Mile 15.1 m/Km)| style="background-color: #FFE183;"|0.041 (217.4 Ft/Mile 41.2 m/Km)| 0.082 (434.7 Ft/Mile 82.3 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 2786| style="background-color: #94CC7D;"|2.013% (106.3 Ft/Mile 20.1 m/Km)| style="background-color: #EDE582;"|0.035 (187.1 Ft/Mile 35.4 m/Km)| 0.071 (374.3 Ft/Mile 70.9 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 1368| style="background-color: #CADB80;"|2.708% (143.0 Ft/Mile 27.1 m/Km)| style="background-color: #FFE383;"|0.041 (214.8 Ft/Mile 40.7 m/Km)| 0.081 (429.5 Ft/Mile 81.3 m/Km)|-| {{Garmin 610}}| 289| style="background-color: #EBE582;"|3.124% (164.9 Ft/Mile 31.2 m/Km)| style="background-color: #CADB80;"|0.031 (166.0 Ft/Mile 31.4 m/Km)| 0.063 (331.9 Ft/Mile 62.9 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 514| style="background-color: #66BF7B;"|1.429% (75.4 Ft/Mile 14.3 m/Km)| style="background-color: #B9D780;"|0.030 (155.8 Ft/Mile 29.5 m/Km)| 0.059 (311.5 Ft/Mile 59.0 m/Km)|-| All| 8605| style="background-color: #D3DE81;"|2.811% (148.4 Ft/Mile 28.1 m/Km)| style="background-color: #FFDE82;"|0.042 (223.2 Ft/Mile 42.3 m/Km)| 0.085 (446.3 Ft/Mile 84.5 m/Km)|-| rowspan="10"|Under Bridge| {{Garmin 10}}| 24| style="background-color: #FFEB84;"|3.387% (178.8 Ft/Mile 33.9 m/Km)| style="background-color: #D8DF81;"|0.033 (174.3 Ft/Mile 33.0 m/Km)| 0.066 (348.6 Ft/Mile 66.0 m/Km)|-| {{Garmin 205}}| 66| style="background-color: #63BE7B;"|-1.379% (72.8 Ft/Mile 13.8 m/Km)| style="background-color: #FA8671;"|0.074 (390.2 Ft/Mile 73.9 m/Km)| 0.148 (780.4 Ft/Mile 147.8 m/Km)|-| {{Garmin 620}}| 61| style="background-color: #FED881;"|4.818% (254.4 Ft/Mile 48.2 m/Km)| style="background-color: #FFE082;"|0.042 (219.7 Ft/Mile 41.6 m/Km)| 0.083 (439.4 Ft/Mile 83.2 m/Km)|-| iPhone 4s| 59| style="background-color: #64BE7B;"|1.402% (74.0 Ft/Mile 14.0 m/Km)| style="background-color: #DEE182;"|0.034 (178.0 Ft/Mile 33.7 m/Km)| 0.067 (356.1 Ft/Mile 67.4 m/Km)|-| {{Polar RC3 GPS}}| 86| style="background-color: #FECD7F;"|5.612% (296.3 Ft/Mile 56.1 m/Km)| style="background-color: #F97A6F;"|0.078 (412.7 Ft/Mile 78.2 m/Km)| 0.156 (825.3 Ft/Mile 156.3 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 222| style="background-color: #F0E683;"|3.193% (168.6 Ft/Mile 31.9 m/Km)| style="background-color: #FECB7E;"|0.049 (260.0 Ft/Mile 49.2 m/Km)| 0.098 (520.0 Ft/Mile 98.5 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 111| style="background-color: #66BE7B;"|1.420% (75.0 Ft/Mile 14.2 m/Km)| style="background-color: #FB9C75;"|0.066 (348.9 Ft/Mile 66.1 m/Km)| 0.132 (697.9 Ft/Mile 132.2 m/Km)|-| {{Garmin 610}}| 22| style="background-color: #CFDD81;"|2.761% (145.8 Ft/Mile 27.6 m/Km)| style="background-color: #FFE984;"|0.038 (201.8 Ft/Mile 38.2 m/Km)| 0.076 (403.6 Ft/Mile 76.4 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 43| style="background-color: #76C37C;"|1.631% (86.1 Ft/Mile 16.3 m/Km)| style="background-color: #F8696B;"|0.084 (444.5 Ft/Mile 84.2 m/Km)| 0.168 (889.0 Ft/Mile 168.4 m/Km)|-| All| 694| style="background-color: #C7DA80;"|2.661% (140.5 Ft/Mile 26.6 m/Km)| style="background-color: #FCA677;"|0.062 (329.0 Ft/Mile 62.3 m/Km)| 0.125 (658.0 Ft/Mile 124.6 m/Km)|-| rowspan="10"|Post Bridge| {{Garmin 10}}| 24| style="background-color: #F97C6F;"|11.616% (613.3 Ft/Mile 116.2 m/Km)| style="background-color: #F9E983;"|0.037 (194.4 Ft/Mile 36.8 m/Km)| 0.074 (388.8 Ft/Mile 73.6 m/Km)|-| {{Garmin 205}}| 66| style="background-color: #9FCF7E;"|2.157% (113.9 Ft/Mile 21.6 m/Km)| style="background-color: #87C87D;"|0.024 (125.5 Ft/Mile 23.8 m/Km)| 0.048 (250.9 Ft/Mile 47The count field is how many measurements I have for that combination of condition and device.5 m/Km)|-| {{Garmin 620}}| 61| style="background-color: #FBA176;"|8.900% (469.9 Ft/Mile 89.0 m/Km)| style="background-color: #FECC7E;"|0.049 (257.6 Ft/Mile 48.8 m/Km)| 0.098 (515.2 Ft/Mile 97.6 m/Km)|-| iPhone 4s| 54| style="background-color: #FFDD82;"|4.422% (233.5 Ft/Mile 44.2 m/Km)| style="background-color: #BCD780;"|0.030 (157.4 Ft/Mile 29.8 m/Km)| 0.060 (314.9 Ft/Mile 59.6 m/Km)|-| {{Polar RC3 GPS}}| 84| style="background-color: #FDB57A;"|7.399% (390.7 Ft/Mile 74.0 m/Km)| style="background-color: #FEC97E;"|0.050 (263.2 Ft/Mile 49.8 m/Km)| 0.100 (526.4 Ft/Mile 99.7 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 188| style="background-color: #FFE283;"|4.095% (216.2 Ft/Mile 41.0 m/Km)| style="background-color: #FEEA83;"|0.037 (197.4 Ft/Mile 37.4 m/Km)| 0.075 (394.8 Ft/Mile 74.8 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 106| style="background-color: #FED580;"|5.053% (266.8 Ft/Mile 50.5 m/Km)| style="background-color: #EDE582;"|0.035 (187.0 Ft/Mile 35.4 m/Km)| 0.071 (374.1 Ft/Mile 70.8 m/Km)|-| {{Garmin 610}}| 22| style="background-color: #FED881;"|4.839% (255.5 Ft/Mile 48.4 m/Km)| style="background-color: #63BE7B;"|0.020 (103.1 Ft/Mile 19.5 m/Km)| 0.039 (206.1 Ft/Mile 39.0 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 40| style="background-color: #FFDE82;"|4.339% (229.1 Ft/Mile 43.4 m/Km)| style="background-color: #73C27B;"|0.021 (113.2 Ft/Mile 21.4 m/Km)| 0.043 (226.4 Ft/Mile 42.9 m/Km)|-| All| 645| style="background-color: #FED280;"|5.287% (279.1 Ft/Mile 52.9 m/Km)| style="background-color: #FFDB81;"|0.043 (228.5 Ft/Mile 43.3 m/Km)| 0.087 (456.9 Ft/Mile 86.5 m/Km)|-| rowspan="10"|Turn Around| {{Garmin 10}}| 23| style="background-color: #F8696B;"|12.971% (684.9 Ft/Mile 129.7 m/Km)| style="background-color: #FFEB84;"|0.038 (198.2 Ft/Mile 37.5 m/Km)| 0.075 (396.5 Ft/Mile 75.1 m/Km)|-| {{Garmin 205}}| 72| style="background-color: #FFE884;"|3.645% (192.5 Ft/Mile 36.5 m/Km)| style="background-color: #9ACE7E;"|0.026 (136.9 Ft/Mile 25.9 m/Km)| 0.052 (273.9 Ft/Mile 51.9 m/Km)|-| {{Garmin 620}}| 80| style="background-color: #FA8070;"|11.302% (596.7 Ft/Mile 113.0 m/Km)| style="background-color: #FFDB81;"|0.043 (228.5 Ft/Mile 43.3 m/Km)| 0.087 (457.0 Ft/Mile 86.6 m/Km)|-| iPhone 4s| 62| style="background-color: #FDBF7C;"|6.623% (349.7 Ft/Mile 66.2 m/Km)| style="background-color: #FED881;"|0.045 (235.6 Ft/Mile 44.6 m/Km)| 0.089 (471.3 Ft/Mile 89.3 m/Km)|-| {{Polar RC3 GPS}}| 92| style="background-color: #FDC27C;"|6.471% (341.7 Ft/Mile 64.7 m/Km)| style="background-color: #FA7D6F;"|0.077 (407.3 Ft/Mile 77.1 m/Km)| 0.154 (814.6 Ft/Mile 154.3 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 205| style="background-color: #FECE7F;"|5.573% (294.2 Ft/Mile 55.7 m/Km)| style="background-color: #FFE082;"|0.042 (219.6 Ft/Mile 41.6 m/Km)| 0.083 (439.2 Ft/Mile 83.2 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 123| style="background-color: #FEC87E;"|6.017% (317.7 Ft/Mile 60.2 m/Km)| style="background-color: #FDBD7C;"|0.054 (285.9 Ft/Mile 54.1 m/Km)| 0.108 (571.8 Ft/Mile 108.3 m/Km)|-| {{Garmin 610}}| 26| style="background-color: #FDC47D;"|6.255% (330.3 Ft/Mile 62.6 m/Km)| style="background-color: #86C87D;"|0.024 (124.7 Ft/Mile 23.6 m/Km)| 0.047 (249.4 Ft/Mile 47.2 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 43| style="background-color: #FED480;"|5.117% (270.2 Ft/Mile 51.2 m/Km)| style="background-color: #98CD7E;"|0.026 (135.3 Ft/Mile 25.6 m/Km)| 0.051 (270.7 Ft/Mile 51.3 m/Km)|-| All| 726| style="background-color: #FDC17C;"|6.523% (344.4 Ft/Mile 65.2 m/Km)| style="background-color: #FDC17C;"|0.053 (279.1 Ft/Mile 52.9 m/Km)| 0.106 (558.1 Ft/Mile 105.7 m/Km)|-| rowspan="10"|Power Line| {{Garmin 10}}| 46| style="background-color: #FCAF79;"|7.841% (414.0 Ft/Mile 78.4 m/Km)| style="background-color: #EFE683;"|0.036 (188.5 Ft/Mile 35.7 m/Km)| 0.071 (377.0 Ft/Mile 71.4 m/Km)|-| {{Garmin 205}}| 127| style="background-color: #64BE7B;"|1.395% (73.7 Ft/Mile 14.0 m/Km)| style="background-color: #83C77C;"|0.023 (122.5 Ft/Mile 23.2 m/Km)| 0.046 (245.1 Ft/Mile 46.4 m/Km)|-| {{Garmin 620}}| 162| style="background-color: #FCAF79;"|7.860% (415.0 Ft/Mile 78.6 m/Km)| style="background-color: #AED37F;"|0.028 (148.7 Ft/Mile 28.2 m/Km)| 0.056 (297.5 Ft/Mile 56.3 m/Km)|-| iPhone 4s| 110| style="background-color: #BFD880;"|2.560% (135.2 Ft/Mile 25.6 m/Km)| style="background-color: #B4D57F;"|0.029 (152.7 Ft/Mile 28.9 m/Km)| 0.058 (305.3 Ft/Mile 57.8 m/Km)|-| {{Polar RC3 GPS}}| 167| style="background-color: #95CC7D;"|2.030% (107.2 Ft/Mile 20.3 m/Km)| style="background-color: #F0E683;"|0.036 (188.8 Ft/Mile 35.8 m/Km)| 0.072 (377.7 Ft/Mile 71.5 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 515| style="background-color: #BFD880;"|2.566% (135.5 Ft/Mile 25.7 m/Km)| style="background-color: #E6E482;"|0.035 (183.2 Ft/Mile 34.7 m/Km)| 0.069 (366.5 Ft/Mile 69.4 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 229| style="background-color: #FDEA83;"|3.360% (177.4 Ft/Mile 33.6 m/Km)| style="background-color: #EEE683;"|0.036 (187.7 Ft/Mile 35.5 m/Km)| 0.071 (375.3 Ft/Mile 71.1 m/Km)|-| {{Garmin 610}}| 43| style="background-color: #FFE383;"|4.038% (213.2 Ft/Mile 40.4 m/Km)| style="background-color: #9ACD7E;"|0.026 (136.7 Ft/Mile 25.9 m/Km)| 0.052 (273.3 Ft/Mile 51.8 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 90| style="background-color: #9BCE7E;"|2.101% (110.9 Ft/Mile 21.0 m/Km)| style="background-color: #8AC97D;"|0.024 (127.2 Ft/Mile 24.1 m/Km)| 0.048 (254.4 Ft/Mile 48.2 m/Km)|-| All| 1489| style="background-color: #F7E883;"|3.281% (173.2 Ft/Mile 32.8 m/Km)| style="background-color: #FFEB84;"|0.038 (198.5 Ft/Mile 37.6 m/Km)| 0.075 (397.1 Ft/Mile 75.2 m/Km)|-| rowspan="10"|Mixed| {{Garmin 10}}| 391| style="background-color: #FCAC78;"|8.030% (424.0 Ft/Mile 80.3 m/Km)| style="background-color: #FCA777;"|0.062 (327.0 Ft/Mile 61.9 m/Km)| 0.124 (654.0 Ft/Mile 123.9 m/Km)|-| {{Garmin 205}}| 1110| style="background-color: #65BE7B;"|1.411% (74.5 Ft/Mile 14.1 m/Km)| style="background-color: #EAE582;"|0.035 (185.6 Ft/Mile 35.2 m/Km)| 0.070 (371.2 Ft/Mile 70.3 m/Km)|-| {{Garmin 620}}| 1308| style="background-color: #FDB67A;"|7.293% (385.1 Ft/Mile 72.9 m/Km)| style="background-color: #FFE082;"|0.042 (220.1 Ft/Mile 41.7 m/Km)| 0.083 (440.2 Ft/Mile 83.4 m/Km)|-| iPhone 4s| 953| style="background-color: #F1E783;"|3.199% (168.9 Ft/Mile 32.0 m/Km)| style="background-color: #F6E883;"|0.036 (192.4 Ft/Mile 36.4 m/Km)| 0.073 (384.8 Ft/Mile 72.9 m/Km)|-| {{Polar RC3 GPS}}| 1412| style="background-color: #BAD780;"|2.495% (131.8 Ft/Mile 25.0 m/Km)| style="background-color: #FDC57D;"|0.051 (269.9 Ft/Mile 51.1 m/Km)| 0.102 (539.9 Ft/Mile 102.3 m/Km)|-| {{Garmin 310XT}} with [[Footpod]]| 3916| style="background-color: #B5D57F;"|2.439% (128.8 Ft/Mile 24.4 m/Km)| style="background-color: #FFEB84;"|0.038 (199.5 Ft/Mile 37.8 m/Km)| 0.076 (399.1 Ft/Mile 75.6 m/Km)|-| {{Garmin 310XT}} no [[Footpod]]| 1937| style="background-color: #E5E382;"|3.050% (161.0 Ft/Mile 30.5 m/Km)| style="background-color: #FFDA81;"|0.044 (231.7 Ft/Mile 43.9 m/Km)| 0.088 (463.3 Ft/Mile 87.8 m/Km)|-| {{Garmin 610}}| 402| style="background-color: #FFEA84;"|3.498% (184.7 Ft/Mile 35.0 m/Km)| style="background-color: #CBDC81;"|0.032 (166.5 Ft/Mile 31.5 m/Km)| 0.063 (332.9 Ft/Mile 63.1 m/Km)|-| {{Garmin 910XT}} with [[Footpod]]| 730| style="background-color: #8BC97D;"|1.900% (100.3 Ft/Mile 19.0 m/Km)| style="background-color: #EFE683;"|0.036 (188.6 Ft/Mile 35.7 m/Km)| 0.071 (377.2 Ft/Mile 71.4 m/Km)|-| All| 12159| style="background-color: #F2E783;"|3.213% (169.7 Ft/Mile 32.1 m/Km)| style="background-color: #FED680;"|0.045 (237.7 Ft/Mile 45.0 m/Km)| 0.090 (475.4 Ft/Mile 90.0 m/Km)|}==Accuracy by Device then Condition=={| class="wikitable"! Device! Condition! Count! Trueness (Average Distance Error)! Standard Deviation! 95% within|-| rowspan="6"|{{Garmin 10}}| Normal| 274| style="background-color: #FCB179;"|7.740% (408.7 Ft/Mile 77.4 m/Km)| style="background-color: #FB9A75;"|0.066 (350.7 Ft/Mile 66.4 m/Km)| 0.133 (701.4 Ft/Mile 132.8 m/Km)|-| Under Bridge| 24| style="background-color: #FAE983;"|3.387% (178.8 Ft/Mile 33.9 m/Km)| style="background-color: #E1E282;"|0.033 (174.3 Ft/Mile 33.0 m/Km)| 0.066 (348.6 Ft/Mile 66.0 m/Km)|-| Post Bridge| 24| style="background-color: #F97C6F;"|11.616% (613.3 Ft/Mile 116.2 m/Km)| style="background-color: #FFEA84;"|0.037 (194.4 Ft/Mile 36.8 m/Km)| 0.074 (388.8 Ft/Mile 73.6 m/Km)|-| Turn Around| 23| style="background-color: #F8696B;"|12.971% (684.9 Ft/Mile 129.7 m/Km)| style="background-color: #FFE884;"|0.038 (198.2 Ft/Mile 37.5 m/Km)| 0.075 (396.5 Ft/Mile 75.1 m/Km)|-| Power Line| 46| style="background-color: #FCAF79;"|7.841% (414.0 Ft/Mile 78.4 m/Km)| style="background-color: #FBE983;"|0.036 (188.5 Ft/Mile 35.7 m/Km)| 0.071 (377.0 Ft/Mile 71.4 m/Km)|-| Mixed| 391| style="background-color: #FCAD78;"|8.030% (424.0 Ft/Mile 80.3 m/Km)| style="background-color: #FCA677;"|0.062 (327.0 Ft/Mile 61.9 m/Km)| 0.124 (654.0 Ft/Mile 123.9 m/Km)|-| rowspan="6"|{{Garmin 205}}| Normal| 779| style="background-color: #63BE7B;"|1.381% (72.9 Ft/Mile 13.8 m/Km)| style="background-color: #D2DE81;"|0.031 (165.6 Ft/Mile 31.4 m/Km)| 0.063 (331.2 Ft/Mile 62.7 m/Km)|-| Under Bridge| 66| style="background-color: #63BE7B;"|-1.379% (72.8 Ft/Mile 13.8 m/Km)| style="background-color: #FA8571;"|0.074 (390.2 Ft/Mile 73.9 m/Km)| 0.148 (780.4 Ft/Mile 147.8 m/Km)|-| Post Bridge| 66| style="background-color: #9DCE7E;"|2.157% (113.9 Ft/Mile 21.6 m/Km)| style="background-color: #8AC97D;"|0.024 (125.5 Ft/Mile 23.8 m/Km)| 0.048 (250.9 Ft/Mile 47.5 m/Km)|-| Turn Around| 72| style="background-color: #FFE984;"|3.645% (192.5 Ft/Mile 36.5 m/Km)| style="background-color: #9FCF7E;"|0.026 (136.9 Ft/Mile 25.9 m/Km)| 0.052 (273.9 Ft/Mile 51.9 m/Km)|-| Power Line| 127| style="background-color: #64BE7B;"|1.395% (73.7 Ft/Mile 14.0 m/Km)| style="background-color: #85C87D;"|0.023 (122.5 Ft/Mile 23.2 m/Km)| 0.046 (245.1 Ft/Mile 46.4 m/Km)|-| Mixed| 1110| style="background-color: #65BE7B;"|1.411% (74.5 Ft/Mile 14.1 m/Km)| style="background-color: #F6E883;"|0.035 (185.6 Ft/Mile 35.2 m/Km)| 0.070 (371.2 Ft/Mile 70.3 m/Km)|-| rowspan="6"|{{Garmin 620}}| Normal| 944| style="background-color: #FDBC7B;"|6.913% (365.0 Ft/Mile 69.1 m/Km)| style="background-color: #FFE082;"|0.040 (213.5 Ft/Mile 40.4 m/Km)| 0.081 (427.0 Ft/Mile 80.9 m/Km)|-| Under Bridge| 61| style="background-color: #FED981;"|4.818% (254.4 Ft/Mile 48.2 m/Km)| style="background-color: #FFDD82;"|0.042 (219.7 Ft/Mile 41.6 m/Km)| 0.083 (439.4 Ft/Mile 83.2 m/Km)|-| Post Bridge| 61| style="background-color: #FBA176;"|8.900% (469.9 Ft/Mile 89.0 m/Km)| style="background-color: #FEC97E;"|0.049 (257.6 Ft/Mile 48.8 m/Km)| 0.098 (515.2 Ft/Mile 97.6 m/Km)|-| Turn Around| 80| style="background-color: #FA8070;"|11.302% (596.7 Ft/Mile 113.0 m/Km)| style="background-color: #FED881;"|0.043 (228.5 Ft/Mile 43.3 m/Km)| 0.087 (457.0 Ft/Mile 86.6 m/Km)|-| Power Line| 162| style="background-color: #FCAF79;"|7.860% (415.0 Ft/Mile 78.6 m/Km)| style="background-color: #B4D57F;"|0.028 (148.7 Ft/Mile 28.2 m/Km)| 0.056 (297.5 Ft/Mile 56.3 m/Km)|-| Mixed| 1308| style="background-color: #FDB77A;"|7.293% (385.1 Ft/Mile 72.9 m/Km)| style="background-color: #FFDC82;"|0.042 (220.1 Ft/Mile 41.7 m/Km)| 0.083 (440.2 Ft/Mile 83.4 m/Km)|-| rowspan="6"|iPhone 4s| Normal| 668| style="background-color: #E1E282;"|3.046% (160.8 Ft/Mile 30.5 m/Km)| style="background-color: #F6E883;"|0.035 (186.0 Ft/Mile 35.2 m/Km)| 0.070 (372.0 Ft/Mile 70.5 m/Km)|-| Under Bridge| 59| style="background-color: #64BE7B;"|1.402% (74.0 Ft/Mile 14.0 m/Km)| style="background-color: #E8E482;"|0.034 (178.0 Ft/Mile 33.7 m/Km)| 0.067 (356.1 Ft/Mile 67.4 m/Km)|-| Post Bridge| 54| style="background-color: #FFDE82;"|4.422% (233.5 Ft/Mile 44.2 m/Km)| style="background-color: #C3D980;"|0.030 (157.4 Ft/Mile 29.8 m/Km)| 0.060 (314.9 Ft/Mile 59.6 m/Km)|-| Turn Around| 62| style="background-color: #FDC07C;"|6.623% (349.7 Ft/Mile 66.2 m/Km)| style="background-color: #FED480;"|0.045 (235.6 Ft/Mile 44.6 m/Km)| 0.089 (471.3 Ft/Mile 89.3 m/Km)|-| Power Line| 110| style="background-color: #BCD780;"|2.560% (135.2 Ft/Mile 25.6 m/Km)| style="background-color: #BBD780;"|0.029 (152.7 Ft/Mile 28.9 m/Km)| 0.058 (305.3 Ft/Mile 57.8 m/Km)|-| Mixed| 953| style="background-color: #ECE582;"|3.199% (168.9 Ft/Mile 32.0 m/Km)| style="background-color: #FFEB84;"|0.036 (192.4 Ft/Mile 36.4 m/Km)| 0.073 (384.8 Ft/Mile 72.9 m/Km)|-| rowspan="6"|{{Polar RC3 GPS}}| Normal| 983| style="background-color: #6CC07B;"|1.511% (79.8 Ft/Mile 15.1 m/Km)| style="background-color: #FFDE82;"|0.041 (217.4 Ft/Mile 41.2 m/Km)| 0.082 (434.7 Ft/Mile 82.3 m/Km)|-| Under Bridge| 86| style="background-color: #FECE7F;"|5.612% (296.3 Ft/Mile 56.1 m/Km)| style="background-color: #F97A6F;"|0.078 (412.7 Ft/Mile 78.2 m/Km)| 0.156 (825.3 Ft/Mile 156.3 m/Km)|-| Post Bridge| 84| style="background-color: #FDB67A;"|7.399% (390.7 Ft/Mile 74.0 m/Km)| style="background-color: #FDC67D;"|0.050 (263.2 Ft/Mile 49.8 m/Km)| 0.100 (526.4 Ft/Mile 99.7 m/Km)|-| Turn Around| 92| style="background-color: #FDC27D;"|6.471% (341.7 Ft/Mile 64.7 m/Km)| style="background-color: #FA7D6F;"|0.077 (407.3 Ft/Mile 77.1 m/Km)| 0.154 (814.6 Ft/Mile 154.3 m/Km)|-| Power Line| 167| style="background-color: #94CC7D;"|2.030% (107.2 Ft/Mile 20.3 m/Km)| style="background-color: #FBEA83;"|0.036 (188.8 Ft/Mile 35.8 m/Km)| 0.072 (377.7 Ft/Mile 71.5 m/Km)|-| Mixed| 1412| style="background-color: #B7D67F;"|2.495% (131.8 Ft/Mile 25.0 m/Km)| style="background-color: #FDC37D;"|0.051 (269.9 Ft/Mile 51.1 m/Km)| 0.102 (539.9 Ft/Mile 102.3 m/Km)|-| rowspan="6"|{{Garmin 310XT}} with [[Footpod]]| Normal| 2786| style="background-color: #92CB7D;"|2.013% (106.3 Ft/Mile 20.1 m/Km)| style="background-color: #F8E983;"|0.035 (187.1 Ft/Mile 35.4 m/Km)| 0.071 (374.3 Ft/Mile 70.9 m/Km)|-| Under Bridge| 222| style="background-color: #ECE582;"|3.193% (168.6 Ft/Mile 31.9 m/Km)| style="background-color: #FEC87E;"|0.049 (260.0 Ft/Mile 49.2 m/Km)| 0.098 (520.0 Ft/Mile 98.5 m/Km)|-| Post Bridge| 188| style="background-color: #FFE383;"|4.095% (216.2 Ft/Mile 41.0 m/Km)| style="background-color: #FFE884;"|0.037 (197.4 Ft/Mile 37.4 m/Km)| 0.075 (394.8 Ft/Mile 74.8 m/Km)|-| Turn Around| 205| style="background-color: #FECE7F;"|5.573% (294.2 Ft/Mile 55.7 m/Km)| style="background-color: #FFDD82;"|0.042 (219.6 Ft/Mile 41.6 m/Km)| 0.083 (439.2 Ft/Mile 83.2 m/Km)|-| Power Line| 515| style="background-color: #BCD780;"|2.566% (135.5 Ft/Mile 25.7 m/Km)| style="background-color: #F1E783;"|0.035 (183.2 Ft/Mile 34.7 m/Km)| 0.069 (366.5 Ft/Mile 69.4 m/Km)|-| Mixed| 3916| style="background-color: #B3D57F;"|2.439% (128.8 Ft/Mile 24.4 m/Km)| style="background-color: #FFE784;"|0.038 (199.5 Ft/Mile 37.8 m/Km)| 0.076 (399.1 Ft/Mile 75.6 m/Km)|-| rowspan="6"|{{Garmin 310XTinclude}} no [[Footpod]]| Normal| 1368| style="background-color: #C7DA80;"|2.708% (143.0 Ft/Mile 27.1 m/Km)| style="background-color: #FFDF82;"|0.041 (214.8 Ft/Mile 40.7 m/Km)| 0.081 (429.5 Ft/Mile 81.3 m/Km)|-| Under Bridge| 111| style="background-color: #66BE7B;"|1.420% (75.0 Ft/Mile 14.2 m/Km)| style="background-color: #FB9A75;"|0.066 (348.9 Ft/Mile 66.1 m/Km)| 0.132 (697.9 Ft/Mile 132.2 m/Km)|-| Post Bridge| 106| style="background-color: #FED680;"|5.053% (266.8 Ft/Mile 50.5 m/Km)| style="background-color: #F8E983;"|0.035 (187.0 Ft/Mile 35.4 m/Km)| 0.071 (374.1 Ft/Mile 70.8 m/Km)|-| Turn Around| 123| style="background-color: #FEC87E;"|6.017% (317.7 Ft/Mile 60.2 m/Km)| style="background-color: #FDBB7B;"|0.054 (285.9 Ft/Mile 54.1 m/Km)| 0.108 (571.8 Ft/Mile 108.3 m/Km)|-| Power Line| 229| style="background-color: #F8E983;"|3.360% (177.4 Ft/Mile 33.6 m/Km)| style="background-color: #F9E983;"|0.036 (187.7 Ft/Mile 35.5 m/Km)| 0.071 (375.3 Ft/Mile 71.1 m/Km)|-| Mixed| 1937| style="background-color: #E1E282;"|3.050% (161.0 Ft/Mile 30.5 m/Km)| style="background-color: #FED680;"|0.044 (231.7 Ft/Mile 43.9 m/Km)| 0.088 (463.3 Ft/Mile 87.8 m/Km)|-| rowspan="6"|{{Garmin 610}}| Normal| 289| style="background-color: #E6E482;"|3.124% (164.9 Ft/Mile 31.2 m/Km)| style="background-color: #D3DE81;"|0.031 (166.0 Ft/Mile 31.4 m/Km)| 0.063 (331.9 Ft/Mile 62.9 m/Km)|-| Under Bridge| 22| style="background-color: #CBDC81;"|2.761% (145.8 Ft/Mile 27.6 m/Km)| style="background-color: #FFE683;"|0.038 (201.8 Ft/Mile 38.2 m/Km)| 0.076 (403.6 Ft/Mile 76.4 m/Km)|-| Post Bridge| 22| style="background-color: #FED881;"|4.839% (255.5 Ft/Mile 48.4 m/Km)| style="background-color: #63BE7B;"|0.020 (103.1 Ft/Mile 19.5 m/Km)| 0.039 (206.1 Ft/Mile 39.0 m/Km)|-| Turn Around| 26| style="background-color: #FDC57D;"|6.255% (330.3 Ft/Mile 62.6 m/Km)| style="background-color: #89C97D;"|0.024 (124.7 Ft/Mile 23.6 m/Km)| 0.047 (249.4 Ft/Mile 47.2 m/Km)|-| Power Line| 43| style="background-color: #FFE383;"|4.038% (213.2 Ft/Mile 40.4 m/Km)| style="background-color: #9ECF7E;"|0.026 (136.7 Ft/Mile 25.9 m/Km)| 0.052 (273.3 Ft/Mile 51.8 m/Km)|-| Mixed| 402| style="background-color: #FFEB84;"|3.498% (184.7 Ft/Mile 35.0 m/Km)| style="background-color: #D3DE81;"|0.032 (166.5 Ft/Mile 31.5 m/Km)| 0.063 (332.9 Ft/Mile 63.1 m/Km)|-| rowspan="6"|{{Garmin 910XT}} with [[Footpod]]| Normal| 514| style="background-color: #66BF7B;"|1.429% (75.4 Ft/Mile 14.3 m/Km)| style="background-color: #C0D980;"|0.030 (155.8 Ft/Mile 29.5 m/Km)| 0.059 (311.5 Ft/Mile 59.0 m/Km)|-| Under Bridge| 43| style="background-color: #76C37C;"|1.631% (86.1 Ft/Mile 16.3 m/Km)| style="background-color: #F8696B;"|0.084 (444.5 Ft/Mile 84.2 m/Km)| 0.168 (889.0 Ft/Mile 168.4 m/Km)|-| Post Bridge| 40| style="background-color: #FFDF82;"|4.339% (229.1 Ft/Mile 43.4 m/Km)| style="background-color: #75C37C;"|0.021 (113.2 Ft/Mile 21.4 m/Km)| 0.043 (226.4 Ft/Mile 42.9 m/Km)|-| Turn Around| 43| style="background-color: #FED580;"|5.117% (270.2 Ft/Mile 51.2 m/Km)| style="background-color: #9CCE7E;"|0.026 (135.3 Ft/Mile 25.6 m/Km)| 0.051 (270.7 Ft/Mile 51.3 m/Km)|-| Power Line| 90| style="background-color: #99CD7E;"|2.101% (110.9 Ft/Mile 21.0 m/Km)| style="background-color: #8DCA7D;"|0.024 (127.2 Ft/Mile 24.1 m/Km)| 0.048 (254.4 Ft/Mile 48.2 m/Km)|-| Mixed| 730| style="background-color: #8AC97D;"|1.900% (100.3 Ft/Mile 19.0 m/Km)| style="background-color: #FBE983;"|0.036 (188.6 Ft/Mile 35.7 m/Km)| 0.071 (377.2 Ft/Mile 71.4 m/Km)|}
==Interpretation and Conclusions==
What do these statistics mean? This is my interpretation:
* The 620 is noticeably poorer than the other devices and the preliminary results of the Garmin 10 are even worse. I found the accuracy of the 10/620 in general usage to be rather grim, and I did some testing pairing them up with the 610 or the 310XT. In all cases the 10/620 would have poor accuracy compared with the 610 or 310XT on the same run. On one run, the 620 lost over a mile over a 28 mile distance.
* The Garmin 610 and Garmin 10 results are preliminary, but I've included them to see if the problems with the Garmin 620 are inherent in a smaller device. The reasonable accuracy I've seen with the Garmin 610 indicates that a small device can have good accuracy.
* The accuracy of all devices is better in a straight line than on curves or bendy routes. My course is a tough test for GPS devices with many curves and only a few relatively straight sections.
* Not surprisingly, accuracy drops going under the bridge.
* More interestingly the trueness just after the bridge is even lower, suggesting that the GPS watches are struggling to reacquire the satellites.
|}
=GPS Short and long measurements=
As you can see from the images below, the GPS track tends to take shortcuts around bends, reducing the length of the measured track. This cutting of the corners indicates the devices are doing some post-hoc smoothing to try to overcome the GPS errors. The more smoothing they do, the better the accuracy is likely to be in a straight line and the worse it is around corners or twisty courses.
[[File:GPS Shortcuts.jpg|none|thumb|500px|The GPS tracks in red with blue dots representing each GPS point recorded. The arrow points to the actual path taken.]]
Often GPS measurements of races, especially marathons record a longer distance than the race. This is partly because the USATF technique for measuring the distance takes a path that is no more than 12 inches away from the tangent (corner), and few runners are able to run that close. In a large marathon you can be forced to take a line that is a long way from the tangent. The other factor is that on a straight line, the GPS error tends to give a slightly longer measurement.
