OK thanks for enlightening me, as a health device the Fenix wins hands down. No argument on that point now.
So this was all about miscommunication.
I tend to take things literally, when it was said, "the motion can't be used for cycling," and knowing it comes with a purpose built handle bar mount, I had to respond. If the statement had been, that the motion doesn't have health data, unlike the Fenix. That would have immediately made sense.
Thanks for your help guys. I understand that the Fenix can't be used for GPSTC but I will use it for results on the water while GT31 is used for the download. Might download the Fenix to KA72 just to compare.
I downloaded the data field, it looks good. It looks like the only thing missing is the nautical mile??
Select to expand quotemathew said..AUS4 said..
ahh - so you want a wrist-mounted GPS that works underwater. Check.
I weep for humanity. 
GOLD 
I'm part of a runners group and I'm amazed how marketing has managed to excuse some shortcomings while hailing the power of the "algorithm". Your watch is great and you are happy about it, perfect. I'm not here to convince anyone otherwise. Sensors are great provided you buy them on top of it. Vendor lock-in is great too, especially for current Suunto users.
Still, in light of what I read above,I'd like to quickly point that Fenix 5X Plus is 51x51x19, Motion is 66x54x16, display is bigger, battery-life is longer, overall accuracy is better, update rate is higher, price is halved. I'll concede it lacks a barometer and sexiness. If anyone lacks something software-wise, I'll add it. It *is* used in other sports. I'm currently adding very low frequency computations for very long trails. I've just removed some constraints for a very fast car.
It's good that we have different options and it's good for these options not to all look alike.
Select to expand quotewdshort said..
Thanks for your help guys. I understand that the Fenix can't be used for GPSTC but I will use it for results on the water while GT31 is used for the download. Might download the Fenix to KA72 just to compare.
You will likely see numbers that are very close most of the time (assuming the Fenix uses doppler speeds, which it probably does). You may see a larger difference (more than 1 knot) maybe every 20th session - more often if you crash and swim a lot, less often if you rarely crash. With about 100 sessions counting just for the 2 seconds ranking, even one error in 20 or 50 sessions would mess up the rankings. On GPSTC approved devices, it's typically possible to identify the artifacts. Without accuracy estimates, that's only sometime possible.
Just a note to watches for other sports and the Motion: for swimming, especially indoors, it's all in the algorithms. Calculating distance and speed from accelerometer data is extremely prone to errors, so if a watch tells you that you swam exactly 2000 meters, it has been using information about typical pool lengths to come up with that number. Not rocket science but works well. For triathlon swimming use (probably a market that's at least 100x bigger than windsurfing), accuracy really just depends on two or three points (end points plus middle if it's an out-and-back swim). Worst case is about a 10 m error - less than 1% in a 1500 m swim. Typical accuracy for a regular-length marathon should be closer to 3 m / 1500 m, or 0.2%. Definitely good enough for any purpose except actually scoring triathlons.
The Motion is very different from Locosys units, and in some respects closer to watches like the Fenix or Suunto. The Motion uses one of the best GPS chips in existence - about 2 decades newer than what's in the GT31. Unlike the Locosys units, it has a lot of computing power on the inside. That means it can easily calculate nautical mile and 1 hour averages. It also means building apps for other sports is entirely possible. We got lucky because Julien is a windsurfer, and made the Motion for windsurfing. Any "market based" approach would give windsurfing resources proportional to the relative market size - perhaps a couple of hours a year. I can think of at least two similar GPS developments that initially had a windsurfing connection which later disappeared because other markets were so much bigger.
Select to expand quoteJulienLe said..
Still, in light of what I read above,I'd like to quickly point that Fenix 5X Plus is 51x51x19, Motion is 66x54x16, display is bigger, battery-life is longer, overall accuracy is better, update rate is higher, price is halved. I'll concede it lacks a barometer and sexiness. If anyone lacks something software-wise, I'll add it. It *is* used in other sports. I'm currently adding very low frequency computations for very long trails. I've just removed some constraints for a very fast car.
All of which make the Motion a better windsurfing device. Unfortunately although you can use it for other sports, it really is not in the same league. You mention the use in cars. I have a Racepak IQ3 Dash on my race car. It does GPS lap timing. The Motion probably has similar accuracy for position/speed tracking to my dash. But my dash connects to the ECU in my car and logs all my engine parameters also, so at the end of a session I can upload and see not only lap times, but cornering Gs, turbo boost, RPM and about 100 other parameters in the same log.
Really, we can pretend the Motion can do other sports and it can... so can my Garmin Geko from 15 years ago. But it is far from optimal for other sports, and really good at "above water" water sports. Really, the Fenix (or other watches like my Vivoactive 3 which is cheaper than the Motion) are much closer to the performance of the Motion for windsurfing than the motion is to them at other fitness sports.
Yes, they bought it as a customized big font display without cables they can re-position or remove at will. They do have ECU real-time peeks and logs for engineers.
