Your seat choice changes your speed test accuracy more than your phone model does. Here is why the window always wins.
GPS signals come from the sky. A window seat gives your phone a direct line to satellites; an aisle seat puts a metal coach body, luggage racks and fellow passengers between you and the signal. In practice: window seats lock faster and hold accuracy under 10 meters, while aisle seats often show 20–50 meter accuracy with jumpier speed.
Train coaches are steel boxes — excellent at blocking radio waves. Your phone near the window catches signals through glass; in the aisle it relies on reflections, which confuse the position calculation.
- Hold the phone up near the window for 10 seconds to get a lock, then keep it there.
- Avoid keeping the phone in a pocket or bag.
- Upper berths near the window side work better than lower aisle berths.
How much difference does the seat make?
Significant — window seats typically halve the GPS error versus aisle seats.
Does coach type matter (AC vs sleeper)?
Slightly. AC coaches with sealed windows still pass GPS fine; the key factor is proximity to glass, not coach class.
What about the vestibule area?
Near the doors signal is decent but the ride vibration makes holding the phone steady harder.
Related: train speed test accuracy and how the speed test works.