Gradual improvement in pace

This lunchtime I sent the 935 back to Garmin for replacement or repair. The barometer module is clearly defective resulting in fixed altitude and temperature readings which are off the (sensible) scale. Before packing the watch I went for a swim at Hatfield but only managed 1.4km before I was getting cold and aware of the troublesome left shoulder.

I've collated the swims recorded over the early one year I've had the watch. The data has been cleaned a little in that I've chosen laps where the GPS data looks valid and without long pauses.

I really am getting a little faster

The data shows a distinct trend for  faster pace. I know that in the pool I've made gains and some of this is translating to the open water but I think that I'm tending to sight better and swim in a more direct line. The GPS track lacks detail in water so small zig-zags aren't recorded as additional swimming distance.

The cluster of faster swims in October 2017 are from Costa Brava where the saltwater gave buoyancy, a HUUB wetsuit was probably faster than my warm and stiff Alpkit wetsuit and finally the guide kayak helped with sighting.

Don't swim with an altimeter

Yesterday I went to check the temperature of the lake at Hatfield (bearing in mind usual limitations of wrist-based thermometers etc) and found that the temperature was a constant 39°C. Now it was a lovely sunny morning but the reported temperature was a more reasonable 13°C!

What I usually see is a drop to a temperature a few degrees above that officially posted.

So I downloaded an app to show the instantaneous temperature from the watch and that showed a fiery 295°C.

Looking back through my data, including runs it then become obvious that the altitude readings had become grossly out of range too, and showing no change on a known hilly route. 

So, a bit of Googling revealed how to get into the service menu and a glance at the barometer check screen confirmed that internal data of the watch was wrong, rather than it being anything to do the Garmin Connect or IQ apps. The temperature and barometer module are linked as ambient temperature is required to adjust the absolute pressure into local altitude. It's worth noting that the watch has another temperature sensor, perhaps on CPU or GPS, which is working fine; but this isn't the one used for user data.

More online searching, ending up on the Garmin Forum, showed that this isn't my unique problem and actually affects other models, including the Fenix. This suggests to me that Garmin use a common subsystem for temperature/altimeter function which is prone to failure. There are at least two devices available including NXP's MPL3115A2 or Servoflo's MS5540 for this subsystem, the MS5540 being waterproof. In this strip-down feature the Fenix's barometer looks rather similar to a MS5540.

Thinking it through, although a barometer device may be rated for 100m salt water use, repeated immersion in chlorinated pool water, occasional salt water and then periods of drying out and perhaps the occasional drop is a very tough environment for a precision micro-mechanical component. Perhaps the whole concept of a multi-sport daily-wear watch is flawed?

Slightly over-egging the journey

So today we're reported as having walked 35 miles although my estimate would be nearer 32 miles. Looking at the track it seems that 'UltraTrac' on the new watch is adding some additional distance through inaccuracy.

This particular view shows small steps, in some areas the track was spot on, in others it was much worse. Nonetheless it's clear that there's some exaggeration going on. This stepping will also explain why the course navigation repeatedly gave off-course alerts. There will always be differences between a GPS record and the real world but this isn't great.

This track, in a wooded valley, is far tighter and was recorded in standard GPS mode. Seems like UltraTrac needs to be used with caution. The issue is that 13 hours walking in UltraTrac took under 40% of battery (I turned off the course function early on as the motor spinning was clearly hammering the battery) but I don't know the relative consumption in ordinary mode. Officially it's around half the longevity.

Bonus!

I spent a salary bonus on a Garmin 935 as my aging Forerunner 110 has remained unreliable despite fitting new battery 6 months ago. Really it seemed very expensive but I took the plunge after noting that it hasn't received hate mail on various Garmin/watch/Suunto forums so it can't be doing too badly.

It arrived fully charged which was nice, but I topped it up via USB nonetheless. Today I took it for a swim which it recorded satisfactorily.

Naturally a few corners are missed off but some of that could be may fault as my sighting technique is poor so every so often I did a little lazy breaststroke. This leaves the watch submerged and thus lacking a GPS signal. This also accounts for the start in the lake as I lost signal whilst dithering in the not-all-that-cold water. I also messed up the cessation of recording but I think I've learn how to do that now. At least Strava does allow cropping.

Today's swim went well too, around 2km but done very slowly. I'm not sure why I'm so slow as I expected the wetsuit to give me pull-buoy-like speed. I know I'm being cautious in the big pond but I didn't think it was that much! Anyway, today I was in the water at just above 14 degrees for an hour so the wetsuit is certainly helping there. Incidentally  the watch recorded the temperature closer to 12 degrees.