Victoria Song: What the Apple Watch Ultra taught me about multiband GPS and failure - The Verge

Traditional GPS requires downloading a satellite’s estimated position in order to begin tracking. That can create challenges if you’re in an obstructed environment. Signals can be corrupted, take more time to download, or get blocked by objects like skyscrapers, canyons, or tree foliage. Mayor says the Ultra can cache orbit predictions for up to a week. That means you can go offline and still get an immediate location fix because you don’t need to wait for your watch to decode that information; it’s already there.

I had no idea that’s how it worked, but that’s very cool.