I don't have a dragy, but this whole temp/attitude DA thing has caused me to wonder where this info is coming from. You are definitely not getting temp or barometric pressue (which factor into DA) from the GPS satellites. If you are getting info from 3 satellites, you can get 2-d mapping (latitude and longitude). When a 4th satellite is available you can also measure altitude (a lot less precisely). But none of this give you temperature or barometric pressure.
It's easy (and cheap enough) for the Dragy to include a barometric sensor and a temp sensor. That would give you enough information to perform the calculation- from within the car! As far as I can see (looking at Dragy docs), it doesn't have external sensors (like a wire leading out of the car), so I can't see how it's getting actual outside temperature unless it's getting the temp from another source.
And that source would have to come from local weather on your phone via the bluetooth connection. That info usually comes from a local airport. And yet, one poster says his is off by 40 degrees. I have searched for where Dragy is getting this info and have not found anything that would explain it.
It would make perfect sense to me from an engineering aspect that the Dragy would have a temp and baro sensor built in. Especially the baro sensor as it could use this to do an uncorrected altitude calculation if the 4th satellite was unavailable.
My point is, the Dragy is definitely going to be quite accurate on its speed/elapsed time info. I would not put much faith in its DA calculation.