well here's a real speed view of the tracks.
The old brain cells are a bit slow these days, and 95% of the time I use the card data from the GTs, that start a new file on power up.
But I've just realised, if you zeroed the GT internal data logger at home, turned the unit off, then traveled somewhere, turned the unit back on and went for a run, then turned the unit off. You'd have an internal data file just like Johno's.
So JP, do you still have the problem if you zero everything at the park, immediately before going for a run?