You probably won't get an accurate reading with publicly available GPS. But you'll get a rough idea.
If we're talking apps and phones then I think 1Hz is as good as it gets generally.in theory within 1/10s, as that's what most them have as a refresh rate. Pretty close IMO.
If we're talking apps and phones then I think 1Hz is as good as it gets generally.
Stuff from Racelogic appears to offer 10 or 20Hz refresh rates, which tallies with what you say, though these are obviously a bit more of an investment compared to just downloading an app on your phone.