Trying to ONLY run 26.2 miles in a marathon (Read 2206 times)

Think of it this way: Let's start with accuracy, you can agree with the best case of +/- 14 feet or even Spaniels +/- 76feet (that'll even make the argument more convincing). Picture yourself running along, draw a circle around yourself with radius of 14 feet (oops, first mistake - it's actually a sphere, up and down must be included). So you're running along and for every point the GPS measures it can have you 14 feet ahead, behind, to the right, to the left, below ground or up in the air. Every single point. The points it measures directly inline with the direction you are traveling will, arguably, cancel out - but not the others. This is why you'll never see a Garmin measure a certified, accurate distance SHORT, it will always be long. Not because of tangents but because of this inherent inaccuracy. Tangents will make it even longer but, unless you were totally crazy about running tangents the longest way possible, I don't see how this could be even close to GPS inaccuracy. No data but that's the reasoning I've come up with as to why I believe GPS inaccuracy is the main culprit in Garmin Forerunner course distance over-measurements. MTA: Caveat - If you have the Garmin set to 'record-every-point' the above discussion stands. If you have the Garmin set to 'Smart Data Recording' a slight mod is needed. In this case, the accuracy will probably be BETTER than 'record-every-point' if there are long sections of straight trail/roadway'. This is because in Smart Recording mode the software will 'decide' whether you are running a straight line and then go back and delete intermediate points (and their inaccuracies) and then interpolate between the two endpoints of that segment. If someone had a accurately, conventionally measured (Jones counter?) 5mile distance (has to be long to get any significant data) on a very straight and flat road or trail you could verify this. I don't think the Garmin would ever measure it short unless it was in Smart Recording mode. In the other mode it would ALWAYS record the distance long and, obviously, would have nothing to do with running any tangents the long way.

From Malmo's discussion of VO2max, but I think it still applies...

The only numbers that matter are the ones that you receive at the end of the race. The most important of these is called place, and is represented as an ordinal. A '1' is the best indicator of your performance. If you get a '1' then you've done excellent. It's no small coincidence that '1' is a homophone for 'won'. Other excellent numbers to receive are '2' and '3'. Not nearly as good as a '1', but by tradition and convention the numbers '1', '2' and '3' are deemed to be the 'supreme ordinals'; that is to say, worthy of gold, silver and bronze, and are segregated from the other ordinals. The rest of the ordinals are represented by the formula: n + 1...(to infinity). There is a direct, inverse relationship between ordinal value and its worth. The closer to the supreme ordinals, the better you've done, the closer to infinity, the worse you've done. One of the other numbers that matters much...is time. Time is always secondary to place in it's value. Neither place nor time are given in the gerbil-wheel lab tests conducted by the exercise-physio-geeks. You will only receive them in the experiment that the real experts call competition. Time does not supersede place, but it is a way of comparing the place of two or more experiments from different venues and eras...

I agree almost 100% (except for the x01 being as accurate as the x0-5), Spaniel! See my post above.

...it is clear that the resulting GPS measurements will never compare to a course certifier with a Jones counter carefully following the tangents of the course...

With this specific point, I agree. Completely. If I've said something that opposes this statement, I have made a mistake, that wasn't my intent. You've all seen my perspective on this subject, so at this point, I am going to head off and look for an Ipod argument to join...

I have learned from this thread that only thing better than geeking out over running stats from the Garmin is geeking out over the accuracy of the running stats from the Garmin.

I don't think Ken was implying that every point would be exactly any amount off, just that it could be. It's also an assumption that a bellcurve of points will be generated. We have no data to tell us what the shape of the curve will be.

I have learned from this thread that only thing better than geeking out over running stats from the Garmin is geeking out over the accuracy of the running stats from the Garmin.

I'm somewhat of a tech geek and this thread frightens me.