When you navigate to the GPS Laptiming menu item, you can set the start/finish line on any (outdoor) race track or circuit, regardless of the sport (from running to motorsports). The start/finish line will then be permanently stored until you overwrite it at some point. To do this, go exactly to the center of the start/finish line. If you later activate the GPS laptiming function, your lap times will be automatically stopped when you cross the line.