Only knows the pool length that you set it to. It's not magic.
?? it is GPS and tracks where I go it is not counting laps, surely?
Garmin 910XT you have to set to the lap distance when you put it on pool swim (there is also the option of open water swim, which uses the GPS). Think it must count each lap when you turn around.
My Garmin 310XT, on the other hand, stops working when it goes in water so it counts no laps.
I was on "walk" I walk faster than I swim!
Was that walking on water??