5S Plus incorrect altitude

First thing first, did you manually Calibrate the Altimeter before starting https://www8.garmin.com/manuals/webh...DAA3358A5.html ? The watch will attempt to Calibrate from map DEM data or GPS at the start of an activity, but they can be substantially off in some environments (DEM can be off if you are on bridge over valley as the DEM data will reference the ground, GPS elevation data is notoriously bad). If you have just manually calibrated the Altimeter before starting the activity, then the 5+ seems respect that over using DEM or GPS.

With regards battery life, the 5S is officially quoted as having up to 11 hours in normal GPS mode https://buy.garmin.com/en-US/US/p/60...01987-00#specs ; so without switching to UltraTrac (which isn’t great for a pretty GPS track, but actually OK for some general navigation needs - do test first though, to check it does what you need) you are already getting as good as it gets for you 5s+ with the 10 hours you got. Unless you have purchased from somewhere that allows you to return and exchange for the 5+ (up to 18 hours) or 5X+ (up to 32 hours), the best thing to do is buy a small USB battery charging block thingy and just charge your 5s+ on the go (you will need to take the watch off your wrist, due to the cable attachment angle, but the activity can be left running/recording whilst charging)ciq.forums.garmin.com/.../1384990.jpg

Crispin - Thanks for your help. I'm planning on a longish hike tomorrow so I'll be sure to calibrate the altimeter at the trailhead. And I've enabled UltraTrac so I will see if that will keep the watch running for longer. I don't really care about the watch's GPS track since I'll be running GaiaGPS on my iPhone.

Will

Climbed Prospectors Mountain which is 11,241 feet high. At the top my watch said I was at 10,800.

The altitude being off by 400' made the watch rather worthless for my primary use

I assume that you started the activity at an altitude which was very different from those 11000 feet?

The Fenix watches use a barometric altimeter. This device calculates the altitude based on these three pieces of information:

• A known air pressure at a known altitude (this is set when you calibrate the altimeter at the start of the activity).
  
• The air pressure measured by the watch at your actual altitude
  
• The assumed density of the air between these two altitudes.
  

This will give you a quite accurate, stable and fast responding altitude without the typical GPS altitude "noise". But there are also two disadvantages:

• If the air pressure at a given altitude is not constant after the calibration, the altitude calculation will drift.
  
• If you go to an altitude which is very different from the altitude where the watch was calibrated, the accuracy of the result will depend on the accuracy of the assumed air density.
  

I guess you were mostly hit by the latter of these two disadvantages. The watch can't know the exact air density between your actual altitude and the altitude used for calibration. This density will depend on the temperature between these two points which it doesn't know. So it has to assume a density, probably based on a known atmosphere model like the ISA model. If this density is off by 5%, then your altitude increase during the hike will also be off by 5%.

Some forum posters claim that the watch will use the internal temperature sensor for calculating the air density. I have done enough testing on my Fenix 3 to know that this watch doesn't. I don't know if your watch does. But I would doubt it, since the internal temperature of the watch can be very different from the actual air temperature if for example you wear the watch under your clothes in cold weather. In such a case, using the internal temperature would cause a larger error than using a standard atmosphere model.

Solutions:
For your use, the GPS altitude in the watch may be better than the barometric altitude. Fortunately, the watch has a data field showing GPS altitude. You can enable this data field in a custom data screen. Unfortunately, the GPS altitude probably can't be logged in the data file, and you can't force the barometric altimeter to be off. So after the hike, when watching the logged trip in Garmin Connect, you will still see the altitudes recorded from the barometric altimeter.

Watches from Suunto use an elevation calculation which is based on both GPS and barometric altitude. In theory this would mean that you get the GPS's advantages of no long term drift during the day, and a much lower error from large altitude variations, and at the same you get the barometric altimeter's advantage of fast, stable and accurate recording of small, quick altitude variations. I don't know how good Suunto's implementation is, but if done well, that would solve all your problems.

Just to pick up on the final paragraph of Allan’s post above, unlike the Fenix 3/5 ranges the Fenix 5+ range do have a Altimeter setting to Auto Cal.>During Activity>Continuous, At Start or Off (the user manual is pretty rubbish at explaining this setting though). The Continuous option should give a similar capability to Suunto’s fused alti, but the 5+ has the advantage of both GPS and DEM data to reference. So might be worth checking you have the Continuous setting on (Menu>Settings>Sensors&Accessories>Altimeter>Auto Cal.>During Activity>Continuous).

I have a Fenix 5x plus. On two very long hikes in the Alps I tried the Auto calibration (set on continous) so far. Before starting the hike I manually calibrated the known altitude. I experienced that the shown altitude always was quite off when I passed landmarks with known altitudes like mountain lodges, alps or summits. It was usually off between 30 to 150 meters (100 to 500 feet) although each time I passed a known altitude I manually calibrated the altimeter to the correct altidude. Very remarkable was when I passed a mountain lodge at 2077 m (6800 feet) and I manually calibrated the altimeter there (altitude was 50meters low, 164 feet). For the following about 300 meters in altidude the altimeter was roughly right then I would say. But then the altimeter suddenly corrected the shown altidude 150 m (500 feet) lower. On the summit then at 2650 m the altimeter showed a bit under 2500m.

I had the Suunto Ambit 3 before with the fused alti technology you described above. That worked amazingly well in ascents. In 3,5 years I never had to calibrate it during an activity in ascents. It always showed the correct altidude on summits for example usually not more than 1 or 2 meters off.in fast descents like with skis or bike the altimeter was sometimes a bit off but not more than 50 meters in altidude.

So what I can say so far the auto calibration on the 5x plus doesn't work that well. I am going to do some more testing, next time with the auto calibration during a mountain hike disabled.

I have a Fenix 5x plus. On two very long hikes in the Alps I tried the Auto calibration (set on continous) so far. Before starting the hike I manually calibrated the known altitude. I experienced that the shown altitude always was quite off when I passed landmarks with known altitudes like mountain lodges, alps or summits. It was usually off between 30 to 150 meters (100 to 500 feet) although each time I passed a known altitude I manually calibrated the altimeter to the correct altidude. Very remarkable was when I passed a mountain lodge at 2077 m (6800 feet) and I manually calibrated the altimeter there (altitude was 50meters low, 164 feet). For the following about 300 meters in altidude the altimeter was roughly right then I would say. But then the altimeter suddenly corrected the shown altidude 150 m (500 feet) lower. On the summit then at 2650 m the altimeter showed a bit under 2500m.

I had the Suunto Ambit 3 before with the fused alti technology you described above. That worked amazingly well in ascents. In 3,5 years I never had to calibrate it during an activity in ascents. It always showed the correct altidude on summits for example usually not more than 1 or 2 meters off.in fast descents like with skis or bike the altimeter was sometimes a bit off but not more than 50 meters in altidude.

So what I can say so far the auto calibration on the 5x plus doesn't work that well. I am going to do some more testing, next time with the auto calibration during a mountain hike disabled.

Which firmware we are talking about?

Firmware is 3.10

Firmware is 3.10

Update to latest beta and your problem will fade off!

Update to latest beta and your problem will fade off!

That is good to hear, thank you, I am going to try it