In article , Scott Williams wrote:
All of my runs involve hills and mountains. There are very few flat
spots to run. I measure out certain distances with my car, 12, 15 and 20
miles but would like a more accurate way to do this.
Important bit of info there. A GPS unit requires 4 signals to give you
credit for altitude gained or lost.
That makes almost no difference, unless you want an elevation profile, but a
GPS will do a pretty bad job at that too (at least as far as running is
Based on measurements I've taken
with my Timex, I'm thinking that it only catches 3 signals, as I come up
short on distance for my hilly workouts, and I'm a flatlander. It seems
to be remarkably consistent with my cyclometer (which is pretty
accurate) on the flats.
I think the errors have nothing to do with the hills. They are more likely to
have something to do with how straight the road/course is (maybe you're going
back and forth in your hill workouts, and it's slicing off distance on your
turnarounds, or maybe the road isn't that straight up the hill) or the quality
of satellite reception. If you only get 3 satellites, it *will* adversely
affect the accuracy of the unit.
FWIW, I have a regular GPS unit, and unless you're on fairly straight roads,
it's not all that accurate. It's good enough for logging milage, but you
wouldn't want to use it to measure your speed.