Check that GPS is enabled in the sport profile you use and if/when it is, just take off the watch and put it outside with good view of the sky after entering pre-exercise mode with the red button. Let it sit fior several minutes and monitor if the satellite searching % is changing. Is it?

You might want to hit up this thread instead: http://forum.slowtwitch.com/...ew_flat;post=5121483

That said, realistically GPS won't be accurate on a tennis court (or barely even a soccer field), doesn't matter who makes the device - a tennis court is simply too small a locale for GPS accuracy in consumer grade devices.

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My tiny little slice of the internets: dcrainmaker.com