I don't have any high tech. But a friend and I went trail riding and she uses Strava (think that's the one). We ended up with a 2 mile difference in distance at the end of the ride (which was 6 miles+) (we both started at zero-me on my cyclometer and her on her app). I double checked my mtn.bike cyclometer against my road bike and both get identical distance readings (I know the road bike is correct-now I know the mtn.bike is also). Guess apps aren't foolproof.