Hi ​@SysMaps,

to avoid misunderstanding: Strava is an app, not a device. Its accuracy is limited by the device it's running on. 

In general, a phone will be less accurate than a watch (speaking of recent multi-band gps watches).

The accuracy may be negatively impacted by multiple factors. For example - the app not having permissions to work on the background; the device being in a low power mode (resulting in less frequent refresh); the device being tucked in a backpack or similar; the activity being done in an area with restricted view of the skies (under a roof, in a tunnel, in a city among very tall buildings etc). All these things may result in a zigzag route instead of a straight line (making the distance longer than it actually was) or cutting corners (making the distance shorter).

If you want to test the accuracy, simply do an activity on a certified distance, e.g. a 10k run, and compare the outcome from different devices / apps. 

There’s also a feature in Strava, but only via the website to recalculate your distance.  Have you ever used this feature?

Thanks I tried this yesterday and it made the tracks even longer. On paper the iPhone and Samsung should be more accurate with more modern multi-band chips (L1, L5 and SBAS) whereas the Bad Elf and Dual simply receive L1 GPS.

Thanks I have checked all of these factors such as background running before snd the Strava tracks were produced on freshly booted iPhone and Samsung models with multi-band capability which should make them more accurate than my data loggers with old technology.