Problems with Altimeter

What is this cheaper sports watch you're comparing against your Instinct?  Make and model? 

Coros Pace 2 

Here are a few things you can work with that may give you a better experience.  First is barometer mode.  Select which best suits the activity you're performing.

• Auto (default setting) - The watch will monitor changes and automatically switch between altimeter or barometer modes
• Altimeter - The watch is locked in altimeter mode and all changes in pressure will impact the elevation reading. This mode is best for activities with a lot of elevation changes. 
• Barometer - The watch is locked in barometer mode and all changes in pressure will be considered due to weather and changes in ambient pressure. This mode is best used for activities without a lot of elevation changes. 

Manually calibrating the altimeter prior to your workout to a known elevation is much better than using GPS.  As already noted, GPS can be off + or - 400 feet.  With this amount of possible error, doing so will most likely give you bad data.  The only time I let the watch calibrate using GPS before my activity is when I'm doing an activity in an area that I don't know the elevation and I hope for the best.  I never use calibrate during an activity for the same reason I mentioned above.  You may start off correctly, hit a point where GPS signal becomes poor, and then the watch regains a good GPS signal and calibrates to where it thinks it is, with that possible + or - 400' margin of error.

I see you're manually calibrating elevation and I'm sure you've noticed "drift".  The barometer can also have this drift.  I can't emphasis enough that when you calibrate the altimeter to a known elevation you need to calibrate the barometer to the correct pressure for that location too.  Easier said than done, but there are phone apps out there that will show you how far you are from a weather station and you can get accurate readings.  If you put in the correct elevation, but the watch is off by .10 inHg on the barometer, once the barometer corrects itself it may think the change was due to a change in elevation.  This is especially the case if there's a rapid change with the barometer.  It's not exact, but a rule of thumb is 50' of elevation change for every .05 inHg change in pressure.

I few other tips that will help with making sense of the data.

a.  Try and spend about 20-30 mins outside where you're going to do your activity before calibrating both the altimeter and barometer.  This will help "climatize" the watch if you're coming from a place where there's a temperature difference.

b.  Note the pressure reading both before and after your activity.  This would easily explain why people see a 100' difference in elevation from there start and finish point if it's the same location.

c.  Keep in mind wind gust, moisture, or any type of blockage of the barometer port will give you crazy measurements.

d.  I'd guess that most user's have the the barometer set to auto mode.  The thing to remember here is the watch is now guessing why there was a change in pressure and it makes altitude adjustments based on that guess.  It's also using other sensors such as the accelerometer for calculations and for the most part it's fairly accurate.  But it can be fooled.  Let's use the example of the barometer being off by .10 on a perfectly surface and you're doing a 2 mile walk.  The barometer will adjust and and see your location and most likely not view this as a change in elevation.  Now, same situation but you're on your bike at a high rate of giddy up.  Because you moved from point A to B so quickly and the pressure changed, the watch is guessing weather doesn't normally change that quickly for that distance, it must be some sort of vertical.  

Just some food for thought.  I hope you find some of this helpful.  Test them out and see how things go.

Thank you so much for your detailed reply. And interesting insights. 

Watch Mode.

To me its not transparent what the modes actually mean. And what constitutes 'a lot of elevation changes'. Does 'Barometer mode' mean GPS only?

I do use 'auto' at the moment, and if my guess regarding 'barometer mode' is correct, this mode would probably give me readings more understandable to me. As I mentioned in the OP I had quite a good experience with a GPS only watch, and got an altimeter to get more accurate.

Calibration during activity.

It's interesting that you turned it off to avoid errors. For me it was the opposite; due to my past positive GPS experience, I turned it on because I thought regular calibration with GPS would at least bring me back to approx the same altitude at the end.

The potential problem you describe is interesting. But wouldn't that typically result in hard jumps or dips? My problem is often more of a steady pull downwards.

Barometer calibration.

I think I see what you are saying, but I don't think I understand or agree. I get why one needs to establish a reference between the current altitude (known) and the current barometric reading (as perceived by the watch). But why does the absolute pressure value matter? In what sense should the barometer be off where it is able to correct itself later? And in that case, wouldnt setting the value introduce a bias once it corrected itself? 

If it's clogged and getting, e.g. too low values and we calibrate it to a higher value, then if the clogging dissolves the reading is gonna jump as well?

Tip b.

Thanks, that is a good idea. I will try that on my next run (hopefully tomorrow). But to me, my experiments sofar indicate a clogging/blocking issue. I can get good readings when not wearing my watch.

Tip c.

Yeah, I think I am seeing part of this. But I can really accept that a 'military grade' outdoor wrist watch becomes unreliable if worn on the wrist and subjected to sweat.

Tip d.

Thanks! Again, I kind of get the point you are trying to make. But don't see what it means for the barometer to be off. I guess I just don't know enough about the algorithm to see how the absolute value would matter. Based on which criteria does the barometer adjust?

Again, thanks for your time! 

henzim said:

But don't see what it means for the barometer to be off. I guess I just don't know enough about the algorithm to see how the absolute value would matter. Based on which criteria does the barometer adjust?

You'll find it explained in details in the document Troubleshooting the Instinct Altimeter and Barometer:

The barometric altimeter on Outdoor watches use barometric pressure to determine changes in elevation, as well as changes to the pressure caused by weather patterns. Outdoor watches will continually monitor barometric pressure to determine which mode is most appropriate at any given time. 

• Auto (default setting) - The watch will monitor changes and automatically switch between altimeter or barometer modes
• Altimeter - The watch is locked in altimeter mode and all changes in pressure will impact the elevation reading. This mode is best for activities with a lot of elevation changes. 
• Barometer - The watch is locked in barometer mode and all changes in pressure will be considered due to weather and changes in ambient pressure. This mode is best used for activities without a lot of elevation changes. 

henzim said:

Does 'Barometer mode' mean GPS only?

Barometer mode just locks the altimeter from going up and down.  The barometer will still read the correct pressure, it just adjust the elevation.  If you're running on a flat track (where you know elevation won't change barring an earthquake :) ), this prevents wind gust or approaching fronts from making the watch think the pressure change was due to elevation change.  It has nothing to do with GPS unless you have the altimeter set to "calibrate during the activity", or "continuous".  I don't know how it's labeled in the Instinct.  Again, I leave this off because I don't trust GPS elevation.  It will use DEM to assist you on your Instinct as long as you have a phone connection, but DEM is only as good as the location the GPS is giving you.

henzim said:

The potential problem you describe is interesting. But wouldn't that typically result in hard jumps or dips? My problem is often more of a steady pull downwards.

It would result in jumps and dips, but that all depends on what GPS elevation is saying.  Not sure why it's mainly dips in your case.

henzim said:

But why does the absolute pressure value matter? In what sense should the barometer be off where it is able to correct itself later?

Depending on how quickly the barometer changes, the watch can misinterpret why the pressure changed.  For example, let's say your known elevation is 600" and you calibrate it to that height.  The current pressure is 30.10 inHg, but your watch is at 29.70.  If you were to walk outside, the barometer is going to correct itself to 30.10.  If it does this faster than a normal weather change, the watch will think the pressure increased because your elevation decreased.  Actually case.  A couple of years back I was in Las Vegas where it was 109 degrees out.  I was walking the strip entering different casinos that where pressurized buildings with the AC at 70 degrees.  The pressure change in this case was so dramatic and quick the watch "assumed" I must have changed my elevation even though it was only a couple of feet.

henzim said:

But I can really accept that a 'military grade' outdoor wrist watch becomes unreliable if worn on the wrist and subjected to sweat.

I don't buy into the sweat blocking the hole either.  Debris yes, but not sweat.  Water with high minerals over time can cause an obstruction too.  I live in the Pacific NW where it's always raining.  I shower and swim with my watch too.  I guarantee it's exposed to more water than the most profuse sweater and I don't have any issues.  I think it's a misunderstanding on how barometric altimeters work and sweat entering and blocking the hole has become the "accepted" reason why people are having issues.

henzim said:

But don't see what it means for the barometer to be off.

The barometer isn't off, it's just not being used for elevation readings when in barometer mode.

henzim said:

Based on which criteria does the barometer adjust?

I'm not sure what exactly what you're asking here.  I can tell you my settings and and I'm always within feet of my actual elevation. 

Altimeter

Calibrate before activity.-OFF-  I manually calibrate every activity.

Calibrate during activity-OFF- 

Barometer

Auto Mode - This is what I usually use since the area I train has some elevation change, but isn't flat.

Altimeter Mode - I use this when Hiking in the Cascade Foothills.  The weather is fairly stable so I want any changes in pressure to record as elevation change.

Barometer Mode - Anytime I'm on a flat track where I know the elevation isn't changing and I don't want changes in weather mistaken a elevation change.

trux said:

Instinct's pressure sensor port is very close to the skin, hence when a pool of sweat builds under the watch, the opening is filled with the sweat, and due to the uncopressibility of liquids, the pressure is immediately transferred to the sensor.

Just as my F6, 945 and 935 do when they're in the rain, shower, pool, lake or ocean.  I'm sure I could manipulate the barometer by adding water to the port and sitting there waiting for a false reading.  But in reality, we're moving and the moisture is easily dispersed and evaporated long before there's a blocking issue.  The port location on the Instinct being blocked by the skin and clothing is far more likely to be the cause of problems then perspiration.  But knowing our history, there's absolutely no doubt in my mind you'll be telling me that I'm wrong. 

Calibrate before activity.-OFF-  I manually calibrate every activity.

Calibrate during activity-OFF- 

Unlike some other Garmin watches, like for example the F6 that offers several modes of "During Activity" auto-calibration (Continuous Mode, At Start, and Off), Instinct only allows On or Off. I am not 100% certain, but from the observation I am persuaded that it only calibrates at the starting point, hence the same as the F6 option At Start.

And, at this type of calibration, there is a rather complex algorithm selecting the elevation for the auto-calibration. And unsurprisingly the previously made manual calibration is used with the highest priority.

In other words, it means that it does not really matter whether you keep the auto-calibration on or off. If you want to keep the absolute control, and are consistent with the manual calibrating, then you can keep the option off. But if you are sometimes lazy, or know that the next elevation options (see them listed below) for the auto-calibration will work well in your situation, then you can quietly keep the Auto-Calibration During Activity on, and continue doing the manual calibration anyway, if you wish - it will be used.

This is the priority list (taken from the document Troubleshooting the fenix 6 or quatix 6 Series Altimeter and Barometer, so it may perhaps slightly differ in some details at Instinct):

1. Manual calibration immediately prior to starting the activity
2. Prior manual calibration point at the same location
3. Recent manual calibration, if the quality of the calibration is determined to be good enough
4. Map data (DEM), if available
5. Prior Connected DEM point at the same location:
   • Connected DEM refers to elevation data from the Garmin Connect app on a paired smartphone
6. Connected DEM, if currently connected to a phone
7. Prior GPS point at the same location
8. GPS, if a good fix has been acquired:
   • After acquiring a GPS fix the timer ring will turn yellow. At that point, it can take up to 30 seconds for the GPS elevation to settle. If vertical speed settles to less than .1 m/s the GPS elevation data will be considered good enough use for altimeter calibration.
   • Before starting the timer, the elevation data field on the watch will preview the calibrated elevation

In contrary, the auto-calibration Not During Activity happens in the sleep hours (usually indoors) using the location of your phone, and the DEM data for the detected location. If you are living in a hi-rise building, or when the phone does not serve a precise position, it may lead to a very big discrepancy. If you regularly see the elevation way off when you wake up, consider disabling the option Auto-Calibration Not During Activity.

trux said:

In contrary, the auto-calibration Not During Activity happens in the sleep hours (usually indoors) using the location of your phone, and the DEM data for the detected location. If you are living in a hi-rise building, or when the phone does not serve a precise position, it may lead to a very big discrepancy. If you regularly see the elevation way off when you wake up, consider disabling the option Auto-Calibration Not During Activity.

Yes, I know.  You learned that from me a while back.  Lol