Everything in LapperSnapper is built on the GPS trace. A few habits make it dramatically better.

Mounting

• Clear view of the sky. Dash, chassis mount, or top of the airbox — not a pocket, not under the seat, not inside a metal enclosure.
• Mount it rigid. Vibration blurs the trace; a hard mount beats a rubber band.

Phone settings

• Keep the screen on while recording. The app requests it automatically, but don't override it — most phones stop delivering GPS when the screen sleeps.
• Disable battery saver for race days; it throttles GPS to save power.
• Location permission: "While Using the App" with precise location on.

Know your source's limits

• Phone GPS updates about once per second — great for lap times, the map, and coaching; blunt for fine corner-by-corner deltas.
• RaceBox records many times faster, and a MyChron adds engine data on top. If you find yourself squinting at small deltas, the hardware upgrade is worth more than any setting.

Symptoms of a poor trace

Lap times that disagree with the board, a racing line cutting across grass, missing laps, or a predictive delta that jumps around — all usually trace back to mounting or screen-off, in that order.