SD constantly seems to calculate a far too high GS. That is my conclusion after caøculating dozens of scenarios.

Here is what i have done:
Android version only supports Static Pilot Log, so I had to create something to have an Operating Flight Plan (=Live Pilot Log). I have asked for support of Live Pilot Log in another thread, but SD answered they can't tell when to support that.

So I created a spreadsheet where I have implemented Live Pilot Log (+ more features than Live Pilot Log). In the spread sheet I enter IAS, temperature, altitude, wind etc. I calculate TAS taking the following into account:
- adjust TAS as a function of temperature and altitude using this formula: http://en.wikipedia.org/wiki/True_airspeed
- increase TAS by 2% per 1000'
- decrease temperature by 2 degC per 1000'
This gives me TAS spot on with the manual E6B (checked with examples on the web). I also compared with the Android app "FlightTools E6B", which is within 1%. So seems my equations are very accurate.

However, SD is constantly giving TAS too high. I compared SD with E6B and my equations by creating routes on SD at different places with different altitudes, temperature and wind conditions. I adjusted the track to get straight tail or head wind (no xwind) such that GS=TAS+/-head wind. Then I looked at the PLOG to get the wind, altitude, TRK and GS data.

Could SD explain why the results differ and how SD calculates TAS taking altitude and temperature into account?

Ok. But SD take the altitude into account, right? Since I notice the higher the altitude, the higher the calculated GS (wind changes taken into account), which means higher calculated TAS. Higher altitude normally means lower temperature, reducing TAS. However, higher altitude also means lower pressure, increasing TAS.

So that may explain why SD calculates a higher GS/TAS than what I get when taking also temperature into account. I'll remove the temperature dependencies from my equations and see if I now get the same GS as SD. I have seen both 2% and 3% being used for increased TAS per 1000 ft. I'll post my results later.