How a phone measures a treadmill run
GPS is useless indoors, so a phone counts steps and multiplies by an estimated stride. What that gets right, what it cannot, and why the number says estimate.
How phone GPS behaves
Runner facing explanation of satellite positioning has been left to fleet telematics vendors and academic papers. These pages write it for people who run.
Articles in this topic
What happens to a run when the GPS drops out
A gap in the track is not a gap in the run. What apps do with missing minutes, why an honest distance under counts, and what a coach should say about it.
What GPS does under bridges and between towers
Underpasses, covered markets and downtown grids each break a track differently. What you see on the map afterwards, and whether the distance runs long or short.
Why two apps measure the same run differently
Same route, same phone, two different distances. Sampling, smoothing, discarded points and the way each app handles a gap explain nearly all of the gap.