Edge 800 or Basecamp data - which is right?

Basecamp rounds up/down so both are 'correct' but the Edge is more exact :)

Thanks. Not sure that I'd consider the "rounding" Basecamp is doing as either logical or consistent. What happens with DIY Audax data - how would you turn the .fit file into an 'accurate' .gpx?

SUSSAMB may well be correct, but it looks a little odd for rounding errors. I am not at all familiar with the Edge line or what types of files it stores. I am also not sure exactly what you are referring to by device vs. BaseCamp. But here are some questions off the top of my head you can think about:

Does device mean real time display?

Is the real time display purely gps data or is it based on a sensor (I have no idea if sensors are applicable, but it would be an interesting idea to incorporate)?

What is downloaded to BaseCamp (a gps track)?

Real time display vs. a stored file for purely GPS data will differ if one logs more points than the other (real time data may update every second, while the saved data is less frequent). More points will translate to a longer distance. The GPS distance should be greater than the true distance.

If the device is displaying data based on a sensor (wheel radius/diameter and revolutions) and downloading a gps track, then you are looking at results obtained by two different methods with different associated errors.

SUSSAMB may well be correct, but it looks a little odd for rounding errors.

Looking at it again I think you're correct and I'm wrong, didn't look closely enough at all the figures, think I must have done it on my phone and probably misread some of them :(