Why this result?

To record the same walk I used two separate mapping apps on my iPhone: Memory Map and Pocket Earth. I started them logging within a few seconds of each other, and similarly at the end of the walk.

MM reported 5.86 miles and PE 5.7. I was about to continue "It was obvious that PE had lost the signal for one wooded section, explaining that difference." But on reflection that doesn't seem to make sense. There's only one GPS chip in the smartphone. So, whatever filtering the apps might do, I would expect them to get the same set of initial trackpoints to work on. If the iPhone was capable of getting a signal in that wooded section (which it plainly was) then why wouldn't PE display it?

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Terry, East Grinstead, UK