Accuracy of GPS devices - Wear them on your head!

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Roo said..
Really don't think it matters too much whether your gps(s) units are mounted on your arm or your head. Doesn't seem to affect the gps records that have been claimed and awarded as there's nothing in the rules to dsq if they are not on your head. Best advice is not to have in under your wetsuit or to stick it down your boardshorts, other than that just get out and windsurf as fast as you can.

Good point Roo, getting out there and doing it is the most important thing for sure.

But there have been some cases with Records where the data was not as good as it could have been and that does affect the error correction figures, some times up to 0.2knots, which is significant when at the records level. We had one Record claim that had to be rejected under the rules because the difference between the two GPS's were too great, clearly caused by poor reception on one of the units. It also has implications for the top rankings in any competitions. It is not something that most of us are normally aware of as we don't look at the error margin figures for out normal competitions and rankings, but I believe it is something we should be doing as soon as the technology allows it.

Testing comparisons with multiple GPS mounted on the head and arm can show some significant differences in less than ideal GPS reception conditions. If you happen to fluke really excellent GPS conditions, the difference can be insignificant, but we are usually unaware of that until we look at the data afterwards, and if you have no other GPS to compare it with you probably would not notice This is especially the case with GPS devices that have less efficient reception or are badly oriented. We are all very happy to accept that 2 second max PB of 35, 40, 45 or even 50 knots and soak up the accolades, but do we ever look at the error range figures and realise that it could be over half a knot out? It's even worse with the Max. speed display! The error range is greatly reduced with a 10 second run and this is a major reason why this was implemented as a GPS standard in the beginning when out GPS devices were very crude in comparison with now. It is further reduced with 5Hz 10 second runs and significantly further reduced with 10Hz, even for 2 seconds! We still have a long way to go to match our accuracy expectations and popular assumptions with reality, but the developing technology is taking us towards that pretty quickly.

But yes, upper arm mounting, done well, has always been an easy compromise for reasonable efficiency most of the time.

I agree with Andrew here, with something like the GT31 that has very good sensitivity, maybe it doesn't matter that much, but the GW52 isn't quite as sensitive and if you want reliable accuracy, it's better on your head.
I tried the PIxie 3 on my head today, but as is my want sometimes I used my head to manoeuvre the sail, this turned the display off and caused havoc with the results.

With the insensitive xperia I definitely get much better looking results when it's on my head.

102 probably has the best reception, I sailed with one inside the wetsuit on my chest and one on my arm and got the exact same results.

Helmet mount done, one (Lindt chocolate box lid) with non slip rubber inserted inside as padding, inserted into helmet and glued, inner helmet padding reinstated with Velcro dots, mesh and screws ( 2x screws have rubber band stretched over middle of phone. Not overly pleased with the look of the mesh fit but it will do until I think of something better.

I knew I was on the right track, several things of the substantial
size, penny dropped, rubber bands of course.

Embedding your GPS in the top of your helmet may give you a more accurate device, but have you thought about what the modifications to the helmet does to its integrity? Presumably you wear a helmet to protect your head during a crash.

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John340 said..
Embedding your GPS in the top of your helmet may give you a more accurate device, but have you thought about what the modifications to the helmet does to its integrity? Presumably you wear a helmet to protect your head during a crash.

Not to mention Alien mind control, I hope you left the tin foil under the Lindt chocolate box. I am picturing a whole bunch of kids on Planet Thwark playing their version of Windsurfing, The Game.