In the sea

My Garmin (Instinct Tactical) can track open-water swimming using GPS (optionally GPS+GLONASS/GALILEO). I selected open water swimming, waited for the satellite signal, and jumped in. After a good swim I got out, looked at the watch, and saw zero.

I stared in surprise and started figuring out what went wrong. GPS doesn't work well underwater. So you have to change your stroke — front crawl instead of breaststroke. I tried the next round doing front crawl and it was immediately better. You do need to kick a bit to let the metres register retroactively… but it works.

I also discovered some amusing things — when the watch locked on to a larger number of satellites the accuracy dropped to within tens of centimetres! That genuinely surprised and impressed me.