Bittner walked ahead of Talbot, stopping several yards away. Talbot squinted through the clinometer and called adjustments—“We can go higher,” he said—until Bittner reached a 10 percent rise, about the limit of a standard treadmill. Then Talbot walked to him while running the GPS tracking app Gaia on his phone, so that as he moved, the app mapped his route up the hillside. By the end of the day, ideally, it would be a track that will become a trail.