En français svp In the twisting vaults of a subway, metro, or U-Bahn, there’s often no reliable cell service, wifi, or GPS. Which means you had no good way of keeping track of your stops or ETA when underground. You had to look out the window for signs on the platform, listen for station announcements, or tilt your neck 90° to read one of those digital screens. How perfectly quaint! Here’s the bad news: we don’t have a hundred billion dollars to build ground-penetrating GPS satellites. The good ...