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GPS jumping or drifting

Short answer

A phone's GPS is accurate to a metre or two on newer dual-frequency iPhones, up to about 5 m on older ones, and it wanders slowly over time, so some drift is normal. Big jumps usually come from a loose mount, a blocked view of the sky or starting before the GPS has settled. If the passes drift over a long job, use the recentre button.

Updated · Oran Dynamics

Jumping (sudden moves)

  • Loose or vibrating mount: a shaking phone gives a noisy position. Use a solid mount.
  • Blocked sky: cab roofs, metal, heated or coated windscreens, trees and buildings all weaken the signal. Move the phone higher, nearer a window, or to a side window.
  • Not settled: open the app a minute or two before you start, ideally in the open.
  • Under trees or beside sheds: expect worse accuracy along hedgerows and yards; it recovers in the open.

Drifting (slow creep)

Phone GPS doesn't hold a fixed error. It slowly wanders by a metre or two over minutes, so a line set an hour ago can appear to sit a metre or two from where you are now.

  • Press recentre to shift the pattern back onto your current pass, keeping the direction.
  • For long jobs on narrow implements, an external receiver paired in iOS improves on the phone's own GPS. See accuracy.

The marker moves smoothly but lags or overshoots

The app smooths the position between GPS updates (about once a second). That works best with the phone fixed solidly to the tractor; a loose or swinging mount can upset it.

Questions

Phone GPS accuracy is a metre or two on newer dual-frequency iPhones, up to about 5 m on older ones, and it changes slowly over time. Recentre the line on your current pass, mount the phone solidly where it can see the sky, and consider an external receiver for tighter work.

Cases rarely do. Metal mounts, coated windscreens and cab roofs can.

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