Cargo Ships Arriving at the ISS Are Guided In Using a Plastic Ruler

You're looking at the European Space Agency astronaut Alexander Gerst as he guided in the Automated Transfer Vehicle 5 to dock with the International Space Station on August 12th. In his hand? A simple plastic ruler.

While ATV-5 is designed to dock without human intervention, someone aboard the ISS always manually checks the approach speed of the massive cargo vessel to ensure that Something Bad doesn't happen. That check involves holding a clear plastic ruler to a display to check the speed. You can see it in his hand. If something had gone wrong. he'd have hit the large red button seen on the docking control panel to abort the docking. Obviously. [ESA]