Drop a flare. Tap the flare button to leave a marker at your own position in the lattice. It stays exactly where you dropped it — fixed in space, not to the Earth — so as the planet carries you along its orbit at about 30 km/s, the flare falls astern within seconds, its distance climbing beside it in the sky. The drop point is set by the direction the Earth is travelling, not by wherever your phone happens to be pointed, so the app turns you toward it first: raise the phone, follow the guide, and the button arms once you are facing the right patch of sky.