Consistent single altitude drop during the training sessions

We need a solution to the problem. It's no use exchanging for the same watch as the problem will continue. Either Garmin exchange the watch for another model that works, or refund what we paid. It's an absurd. First they have already disabled the temperature measurement in swimming pool. This indicates that you identified an initial problem there, but did not resolve it and attempted an interim solution. The problem affects everyone and we need a solution from a company like Garmin.

I did as Kevin suggested and contacted support. I was prepared to cover the extra cost and replace the watch with a 255 or add more for a 955. Support offered me a new 745, which is fair enough. I understand others reluctance to take another 745 as a replacement, but hopefully the problem is as they claim, limited to a few watches.

In fairness to Garmin, I've always found them fairly reasonable when it comes to issues with a watch. I switched from Polar to Garmin years ago, I have gone from a 30 to a 645, to my current 745 and will more than likely buy another in a couple of years. As in life folks, don't be a d**k with support and they will look after you.  

It's nice you are satisfied and you were ready to pay something extra and replace the watch with a 255 or 955. I am not ready to pay something extra and exchange them for another model. I'm happy with the 745 and don't want to change them. I know 4 people in my area who have 745's and they all have the same problem so I don't think it's really a problem of a few watches. And therefore, even exchanging it for a new 745 will not help. I wish you satisfaction with the support and I will certainly not behave inappropriately towards them. I'm just waiting (a quarter of a year) for some working solution :)

I am also quite sure that exchanging the watch to another 745 won't help since the issue appears to be rather software- than hardware-related.

At least when speaking of my own 745, I can say that the altitude drops did not happen in older firmware releases. I have not yet found the time to analyze by downgrading when the issue exactly appeared.

By the way, the just-released beta (11.73) did not change anything. I had a 45 meter drop in the first kilometer of today's run.

Yesterday I ran my first marathon with a consistent 100m altitude offset throughout the whole race, so at least I didn’t experience the sudden drop in altitude. Wasn’t auto calibration at the start of every gps activity introduced a few months ago?

https://www8.garmin.com/manuals/webhelp/GUID-2492EDA1-1182-400B-8F43-D8B3211E4F3C/EN-US/GUID-CDC9DDEE-C576-4E1D-B007-BC737686793A.html

Maybe it is not important, maybe is...so I am asking, why in my FR 745 is the barometer setting different from official Manual... Because I have the Watch mode in Altimeter setting not in Barometer setting. So it sets different sensor? Could this be potential cause of the problem? 

Same here. The setting under "altitude" seem to be comparable however. There you can set "automatic" "only barometer" or "only altitude".

Hi Kevin,

I had a race last weekend where I experienced this phenomenon - around the 38 minute mark, a drop of around 50meters happened in 1 second.

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I have had the watch for around 1 1/2 years and this has never been a problem till recently. What I think is really interesting here is that the older brother FR 945 does not seem to have this problem. The large difference between the two is built-in maps. And both the FR 745 and 945 have the same update schedule with very similar fix-logs. I too think this can only be an auto-calibration kicking in at the wrong time. The Edge 530 fixes this kind of problem by locking to the start elevation (even if is wrong) and holds this thru the duration of the ride. But I too would be appreciative to see this fixed, and would even welcome reverting back to the last update that did not have this problem in June this year.

Thanks,

Jamey S

I've had another dig through the data I have, and it looks like this was an issue introduced when the v11 firmware was launched.  For me all runs up to and including 28 of June on Firmwares upto 10.40 all look ok...  From the 29 of June on firmware 11.03 the issues start to show.

11.03 was itself a beta an alpha, the first public one for v11 if I'm correct... as such it seems that the issue arose as part of the relatively large change from v10 to v11.  A few of us did report it in the alpha forums for 11.03 in June and July, and then again in August for 11.04 in August.  However I guess the noise wasnt loud enough at the time (just a handful of beta testers raising the issue), so it made it into the production firmware :-(

Hopefully this helps in some small part enabling Garmin-Kevin and team finding the root cause.  Although I dont think the published change log will be too helpful as I believe that any altimeter change might have just been listed as bug fixes; and I also suspect that some changes were applied in v11 in the background, but not made visible to the user until a little later.

My personal pet theory is that the 745 being a mid cycle product has some unique or slightly different hardware as compared to the 945 or the later 945 LTE and as such when the v11 features were packaged up, a change which was needed for the hardware in a different watch were accidentally copied into the 745 branch.  Looking at the wonky data recorded since v11 makes me think that the overall calibration factor is incorrect (exagerating any alt change), and as such the jump we are seeing is when the watch tried to auto correct as it is intended to do (although usually these woudl be small and to compensate for temp changes not calibration errors).

It looks like I've been a bit of a hoarder, and i still have the beta 11.03 firmware sitting in my downloads folder, which more interestingly includes the 10.40 firmware as a downgrade option.  If anyone would like to take a look themselves then the files can be downloaded from https://www8.garmin.com/support/download_details.jsp?id=15459

I should caution that I'm holding off on attempting any downgrade myself as I know a number of other modules have been upgraded in more recent changes on the watch (GPS, sensors etc) so I think the downgrade is only intended if you are moving from 10.40 to 11.03 and back... since the other modules arent included, the downgrade wont be exactly the same as reverting to 10.40 even if you can get it to work....

I did the same digging yesterday, and actually, I found something interesting. In the past few months I've been using the 745 primarily for running as I was training for a marathon, and it seems like the altitude drops or jumps occur randomly, without no specific cause or reason. I did however record a few cycling sessions as well. In particular, the last one I did was on Aug 18, just a few days after FW 11.10 was released, and this was actually the first time where the altitude bug showed up. Now, in my specific case, I can confirm the altitude jump did not occur at a random spot, but right at the start of a very short sprint I did on a very flat and straight road. As you can see from the attached image, a sudden jump in altitude from 65 to 92m overlaps with increased heart rate and speed as I was starting my sprint. I always keep my 745 firmly attached to the handlebar when I'm cycling and I use the HRM-PRO to monitor my heart rate. The speed data comes from the Speed sensor 2. Garmin-Kevin could this be helpful to you?