Calculating the distance run

[CharlieCrock]

How does the Surge calculate the distance run?

I have run twice in the last week.

Number of steps was almost identical, 4,575 v 4,576, but the distance reported on my Surge was 0.19km different, 4.82km v 5.01km.

Running stride is set to 90cm.

The Fitbit HELP (https://help.fitbit.com/articles/en_US/Help_article/1135) says:

'Fitbit trackers calculate distance by multiplying your walking steps by your walking stride length and multiplying your running steps by your running stride length'

... but the calculations imply this is not the case.
Can anybody help?

[SteveH]

The problem is that we don't know when fitbit chooses to use the walking stride and when to use the running stride. It may be that your pace dropped at some point and it switched to the walking stride for some of the steps.

[CharlieCrock]

Thanks for the comment Steve.

I was in Run Mode, so would expect the Surge to use the stride length for Running.

Do you know the actual algorithm used to calculate distance?

[SteveH]

It's different if you use run mode rather than just let your fitbit track a run. If you just wear your Surge and go for a run then it uses the steps x stride calculation but in run mode you can choose to use GPS and it will use that instead. Did you have GPS enabled on your run? See this help file for info:

https://help.fitbit.com/articles/en_US/Help_article/1142/

[CharlieCrock]

Steve - yes, I have GPS enabled all the time.

Each time I run, I choose Run Mode and wait to connect to satallites before starting.

Are you suggesting 'tracking a run' is more accurate, especially when running under trees etc ?