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Altimeter Discussion

Former Member over 6 years ago

I have owned a Garmin 935 from almost when they 1st came out. Before the 935 I have a Fenix 3 HR, before that a Garmin 920XT and others before.

I really want to like the the 935, I love the size and weight of it, the battery life, the fit, the operating system and I like the idea of what its meant to do - I say idea of what its meant to do because I find it horribly unreliable. I have a spoken to Garmin support many times and I have even been sent a replacement watch and I have always been on top of updates, but I have no resided the fact that the watch is not very good by design.

Like everyone else I have massive problems with the Altimeter, every activity I record that is on land I get inaccurate information about altitude. My Altitude may start out correctly (I will often re-calibrate before an activity as its reading wrong), but the activity will always end with -36 or something like that. Why or why Garmin can my watch only use the Altimeter for Altitude? Your cheaper watches use GPS and I have found this far more accurate (my GF's watches she has had).

9 out of 10 sea swims I will get poor GPS data from, its usually very erratic, it usually looks like its only recorded half the distance or just draws dead straight or erratic lines. I have tried all satellite combinations but no luck. Sea swimming is probably the biggest failure of the watch. My GF's cheaper 735XT usually has no problems with sea swims.

Any running or cycling activities that might be over 4 hours - there will be a high chance of GPS failures here. GPS may drop signal for 5 - 10 minutes for no reason, in broad day light with no hills or trees in sight. I have also seen my GPS say i'm riding 100kms per hour when i'm stood still. Once again I have not seen these issues on my GFs 735XT. I have tried many different settings and satellite combinations but no good.

I have a few friends that own this watch but they don't see any issues, but they use their 935's for running and usually nothing longer than a couple hours.

So why dont I switch to a 735 you ask? Well I need the long capacity of the battery as many of my activities are long distance.

What do other people use and do that may have the same issues as me? Do you recommend other watches and what watches? The Fenix 3HR I felt too big on my wrist and caused me a bit of pain on my skinny wrists. I have heard the Fenix 5 has problems too, I dont know anything about the Fenix 5 Plus except its very expensive.

0 Steph74-74 over 6 years ago

you are lucky to have altimeter working fine.
Mine is always giving bad information. I will then recontact Garmin support if it is a harware problem. I always thought it was sofware bug.
You can see enclosed my last run with altitude comparison between the watch and real altitude. light green is watch altitude. I finished my run with almost 100m more than the starting point on the same place. I had in parallel another altimeter without any problem so no variation of barometric pressure during this run that could explain such a variation. We can nevertheless see that the altitude profile is quiet corresponding but with an increasing offset ...

0 Former Member over 6 years ago

Steph74-74 I disagree. Before you dismiss my response, please hear me out. I was seeing off altitude readings when I first got my 935 which confused me too. After raising questions on this forum, I was enlightened on how a barometric altimeter works from a fellow forum user and decided to do my own research. After the 16:40 minute of your graph, your altitude changed between devices, but the difference in altitude between the two was the same and gradually climbed at the same rate for the remainder of your activity. This tells me the two had a different barometric reading from the 16:40 point on. Your graph is too symmetrical to suggest otherwise.

0 Steph74-74 over 6 years ago

TMK17, I do not understand the end of your answer.
I know how a barometric altimeter works and as I said in my post I had another barometric altimeter during my run to check the difference between the watch and the other one.
If barometric pressure lowers during the run. It might explain this increase in altitude. A variation of 12 or 13 mb could explain this increase of 100meter . (1mb = 8.3 meter). but the weather was constant during my run. Weather forecast was not announcing any big pressure variation in the area of the run and the other barometric altimeter give the same altitude at the end of the run that the starting altitude of the circuit.
With this information, I think I don't do any mistake concluding that the altimeter of the watch is having problem. It is either barometric pressure accuracy of the probe that is not good or some pressure misreading due to the position of the probe inside the watch.
I agree that it is not completely wrong because the shape of the curve is quiet correct. Perhaps Garmin can help explaining us what could happen.

0 AllanOlesen67 over 6 years ago

I will say the same as I have said in a number of other threads: Start by enabling Ambient Pressure in a data field. (Not Barometric Pressure). This is the key to understanding what is going on.

If you are at the same altitude at the end and start of your workout, and you know from other sources that the air pressure at that altitude did not change during that time, two things can have happened:

1. If the Ambient Pressure datafield shows another value after the workout, then you have a sensor problem of some sort.

2. If the Ambien Pressure datafield shows the same Value after the workout, and you have another altitude reading, then you probably also have another Barometric Pressure reading. In this case, the firmware in the watch did some wrong guesses about the reason for the changes in ambient pressure during the run, thinking that some of them were caused by a general change in air pressure while they were in fact caused by an altitude change, or vice versa.

Without the information about the Ambient Pressure reading, every attempt of finding the reason is guesswork. And in most threads it stays at the guesswork, because people aren't really interested in finding out what is happening.

0 The_Hunnymonster over 6 years ago

And in most threads it stays at the guesswork, because people aren't really interested in finding out what is happening.

Too true!

0 Steph74-74 over 6 years ago

Thank you for your answer.
I will investigate on my side. Altitude is an important information for me because I live in the mountains. I was not aware of this field "Ambient pressure".

I also put my watch into "altitude mode" instead of auto mode because I am not interested in the barometric information and my activities are sufficiently short (one to 3 hours max) not to be very concerned by barometric variations.

What I can already see is that just by removing my watch from the wrist and putting on a table for 5 minutes change the "ambiant pressure" from +2 hpa and so change the altitude for approximately -20 m.
Is there any issue with temperature of the watch also ???? big mystery with this feature ...

0 Pierrotsc over 6 years ago

i thought the watch had 100 feet variation. the watch uses the gps to find the location. i am biking along the ocean and i should have an altitude of zero. i do not. i think it may show 100 feet or so. but it is consistent along the ride. should i get a zero altitude ?

0 Former Member over 6 years ago

Pierrotsc If you calibrated the altimeter to the correct known elevation and the barometer to the current pressure, yes your watch should read a few feet above sea level. Keep in mind, depending on what mode you have the barometer in, changes in pressure/temperature will change your elevation accordingly. If your entire ride is along the ocean, you can set the mode to barometer. This way any changes to the barometer will be seen as pressure changes and not elevation changes. I posted a thread a few weeks back and never got an answer. I believe when you are in an activity, the mode defaults back to auto.

0 Pierrotsc over 6 years ago

TMK17 i never played with the altimeter or barometer. i just start my ride after getting a lock on the gps. should i go under altimeter or barometer widget and tell it to calibrate ? to tell you the truth, i never bother to go there but i can try to see if i get a correct elevation starting my ride. thanks.

0 Former Member over 6 years ago

should i go under altimeter or barometer widget and tell it to calibrate?

Go into settings, sensors & accessories. Select altimeter to set your elevation only, or select barometer and you can set both elevation and pressure.