If you use a GPS watch on a track, you are an idiot.

GPS Man wrote:

I always find it interesting that if I run in the normal counter-clockwise direction the distance comes up different than running clockwise. For example...mile repeats yesterday. First repeat in the normal direction measured at 0.99 miles. Second repeat going clockwise measured at 1.07.

That's not an error, it really is farther to go clockwise, due to the rotation of the Earth. But only in the northern hemisphere.

GPS is operated by the US Air Force and must meet performance targets set by the US Government. these targets relate to the accuracy of the signals sent from space.

the manufacturer of your device is responsible for the accuracy with which those signals are translated into position data, the accuracy of any time calculations, and the accuracy with which that data is displayed with mapping or other software.

therefore, when considering the accuracy of your position as determined by your watch, there are two different accuracy determinations to be made. and, it is worth noting that it is impossible for your device to display your position more accurately than the signal itself. by law, the signal has to be sent with a global accuracy of

for some reason the bottom of my post got cut off...

I wouldn't go as far as to say that anyone using a GPS watch to collect data on a track session is an idiot, per se, but they are certainly deluding themselves over the utility of the toy they are playing with. it is useful for telling the coastguard where you are so they can come rescue you, and it's useful for finding coffee shops and libraries, but if you need a watch to tell you how far one lap of a running track is then you have more important problems than the accuracy of your watch.

cheers.

https://www.gps.gov/systems/gps/performance/accuracy/#speed

https://www.ion.org/publications/abstract.cfm?articleID=13079

I am obviously having a senior moment because that's twice it didn't work... so here goes thrice (it turns out there were math symbols the software didn't like).

GPS is operated by the US Air Force and must meet performance targets set by the US Government. these targets relate to the accuracy of the signals sent from space.

the manufacturer of your device is responsible for the accuracy with which those signals are translated into position data, the accuracy of any time calculations, and the accuracy with which that data is displayed with mapping or other software.

therefore, when considering the accuracy of your position as determined by your watch, there are two different accuracy determinations to be made. and, it is worth noting that it is impossible for your device to display your position more accurately than the signal itself. by law, the signal has to be sent with a global accuracy of less than or equal to 7.8m, with 95% probability. the US Air Force exceed that target most of the time. for example, on May 11 2015, the global average signal accuracy was less than or equal to 0.715 metres (2.3 feet). I repeat, it is impossible for your watch to be more accurate than the signal.

a MOOC is a Massive Open Online Course, it is a college level course offered online to anyone who cares to participate.

in 2015 a MOOC on GPS navigation conducted an online experiment to determine the accuracy of mobile phones. over one thousands students in over a hundred different countries participated in the experiment and they found that, on average, their devices returned their position with an accuracy of 4.9 metres. that puts you somewhere inside a circle 32 feet across.

I wouldn't go as far as to say that anyone using a GPS watch to collect data on a track session is an idiot, per se, but they are certainly deluding themselves over the utility of the toy they are playing with. it is useful for telling the coastguard where you are so they can come rescue you, and it's useful for finding coffee shops and libraries, but if you need a watch to tell you how far one lap of a running track is then you have more important problems than the accuracy of your watch.

https://www.gps.gov/systems/gps/performance/accuracy/#speed

https://www.ion.org/publications/abstract.cfm?articleID=13079

cheers.

Just for kicks I downloaded Strava and took it on a bike ride to compare it to my well-calibrated and accurate odometer.

Over a significant distance, it was over by nearly 4%. Judging by the path it drew, it looked like this was because of exaggerated side-to-side weaving that didn't happen. I think if you cross a certain boundary it says you moved X distance even if it was really only 1 meter.

But the real hoot was it auto-pauses the timer whenever you stop, dramatically reducing elapsed time and increasing average speed.

Technoidiot wrote:

Your GPS isn't that accurate idiot.

You must just have a cheapo watch. Mine gives the same measurement as the track, pretty much to the meter. Plus is useful if your not running in lane one.

I've tested a number of GPS and accelerometer devices/apps. I test them on a 400m track (open space, adding the extra 9M per mile) and on a wheel measured course. If you are judging your fitness from a GPS or accelerometer/app device you are probably not as fit as you think you are. They all get the distance wrong (under distance), so you think you are running faster than you really are. If you are finding that your races are harder than you think they should be, or you are blowing-up in marathons, you're probably not capable of racing at the pace that your devices is indicating you are training at.

The best GPS I repeatedly tested (Garmin) was 80M - 120M less over 4 miles, which is good, but not good if you're training to race a track 5k. Accelerometer apps tend to test worse, some much worse (50% short). They all test better over courses with longer straights and broader turns, but only if trees or buildings aren't interfering. If you really want to know how fast you're going, go to a track or run on a measured section of path or road. Otherwise, you should probably add some seconds per mile to what the device is telling you.

Radical CJ wrote:

Technoidiot wrote:

Your GPS isn't that accurate idiot.

You must just have a cheapo watch. Mine gives the same measurement as the track, pretty much to the meter. Plus is useful if your not running in lane one.

My watch was 6 million dollars so I highly doubt that

WinnythePoo wrote:

Agreed. I take my watch off and leave it just outside the track, usually clipped to the fence. Hasn't been stolen yet!

Which track do you usually use and what days and time are you primarily there?

I guess if you run 400m in say lane 4 from the start line and stop at the finish line the device should say 400m were covered. Anything other than that would prove that the device is not accurate since we know that the white line is a precise 400m. I would also say that the watch needs to be on your left wrist which needs to be as close to the white line as possible.

My watch has precision down to .01 of a second and seems to be accurate to at least .1. Verified with several stopwatches. Not sure what the problem is here...

Too many people pooped under the bleachers at our track so it is no longer open to the public

Radical CJ wrote:

Technoidiot wrote:

Your GPS isn't that accurate idiot.

You must just have a cheapo watch. Mine gives the same measurement as the track, pretty much to the meter. Plus is useful if your not running in lane one.

Do you have some military grade watch that the rest of us can't buy? Pretty much every track workout you see on strava looks like this if not worse:

Idiots.

800 dude wrote:

Technoidiot wrote:

Your GPS isn't that accurate idiot.

Yes it is. GPS does very well on a track because there are no sudden hairpins or sharp turns and rarely any tree cover.

ditto

I use mine on the track and it's very accurate. There is no better place to determine accuracy than on a track, obviously. It helps with pacing longer intervals if you've never actually been on a track team. It's not like you stare at it, but a glance ten seconds into the interval lets you know if you're on track. Not everyone has the experience to know by feel.

Nigel_Bikes wrote:

I guess if you run 400m in say lane 4 from the start line and stop at the finish line the device should say 400m were covered. Anything other than that would prove that the device is not accurate since we know that the white line is a precise 400m. I would also say that the watch needs to be on your left wrist which needs to be as close to the white line as possible.

Why would what wrist matter when your GPS is only accurate to +/-5 meters? That means for every sample (every lat/long pair) you have to draw a circle of 5m radius around the point and that's your possible location. How would the GPS know the difference between 0.75m (distance between wrists) when 5m is the best accuracy you can expect from a consumer GPS watch?

You want accurate GPS? Use an RTK setup. Precision and accuracy within 20cm or better.

Winny, your original post said nothing about why you think a person is an idiot for "wearing" a GPS watch on a track. I will infer that you think it would be stupid to, say, plan to run 800m repeats, but stop at 750m if the watch said "0.5" on it.

How many people out there do that? If I'm going to do an 800m run, I run two laps and click the lap button as I cross the line. It's remarkable that the GPS watch actually calculates time, and not just distance. I record that time in my training log. At the end of the day, I don't really care if the total distance on the watch is a few tenths of a mile off in one direction or the other.

WinnytheBish wrote:

Idiots.

^^This. GPS is not even close to "accurate." Nor is it necessary in any way on a track. The f*cking thing is marked for distance. How difficult is this to comprehend?!?

yup.... wrote:

WinnytheBish wrote:

Idiots.

^^This. GPS is not even close to "accurate." Nor is it necessary in any way on a track. The f*cking thing is marked for distance. How difficult is this to comprehend?!?

if it's not accurate then why does my watch say 800m when I ran 800m on the track?