If you ever have need to accurately measure the true airspeed of your aircraft, I have created an android app (MeasureTAS) that makes it very simple to measure true airspeed to GPS accuracy. This app is based on a popular algorithm developed and published in 1998 by Doug Gray. The app is available on the Google Play Store - it is free and without ads. There is a link to Doug Gray’s paper on the MeasureTAS page on Google Play.
Does it involve flying a triangular course?
You fly legs in three arbitrary directions (preferably spaced 90-120 degrees apart). The app captures track and groundspeeds and performs the calculations.