Stryd calibration changed

mcalista said:

Given that GPS has a circular probable error of 5 meters, I'd love to know the use case for knowing GPS distance to the centimeter.

We are not talking about GPS distance. It is calibration of a Stryd foot pod for distance using a known distance as reference. By comparing the measured distance, in this case 4000m against the distance measured by Stryd, 4036.61m, you will get the calibration factor which is 99.1 ( (4000/4037) * 100 ).

p50kombi said:

Any idea where I can find the stryd calibration used in a Fit file? 

Yes, I do. First I should say that this is based on doing my own analysis of the FIT file and not documentation...

First export the FIT file using the SDK and import to Excel. Once in Excel there are two rows; First a row with device info and then one row with the device configuration/pairing info:

In Yellow you find the device info that tells you this is a Stryd, I verified that by looking at fit_profile.hpp in the SDK. Perhaps it is documented in a more user friendly format than in source code...

In purple there is an ID which I think is internal and unique to every pairing with the watch but you can use that one to find the configuration. In blue you have your AntID (I suppose you paired using Ant and not BT) and finally in green you have the calibration factor.

mleonc92 said:

Did you solve your problem with Stryd autocalibrating itself?

Yes I did. With some perspective I realised that I must have mixed the numbers and entered the wrong number in the first place. 4037/4000 instead of 4000/4037, I also verified by looking inside the FIT file for my first run after calibration.

As a note I did the same calibration run in July this year and got 98.1. For consistency I kept the calibration at 99.1. I also think that the small difference is within error margins for not running absolutely straight.

https://connect.garmin.com/modern/activity/7040022994

Thanks for the explanation of Stryd wonky behavior when I go on a dog walk after a run and still have the Stryd on my shoe. I had taken to using a custom power profile to disconnect accessories when I go on a walk with my Stryd still connected to my shoe. 

Now it makes sense. 

Hi. That's interesting and I found my calibration factor, but if I change it during a run, I don't see where is the new calibration factor. For example, I ran using 99.4 as calibration factor, but then change it to 97.4 and 96.4, but there is only "994" in the whole file. When I search for "974" or "964" I get nothing.

It only uses the new calibration factor on your next run, you can't adjust it mid run as far as I know. 

I can adjust it during a run and it measures different after the change, but maybe in the file, instead of saying "984" and in another line "974", it says something like "-10"

mleonc92 said:

but if I change it during a run, I don't see where is the new calibration factor

I have never tried, what is the reason for changing during a run?

I have noticed that during the first 4 minutes, Stryd always measures me around 2% less. Something similar happened to me with Garmin foot pod. I think it can be related with the fact that my cadence is always higher at the start.