If you’re like me and always staring out the plane window you no doubt have seen two numbers (between 01 and 36) at the ends of a runway. What do they mean, you might wonder? This two-minute video by Tech Insider will tell you the answer (and you don’t need to have the volume on since it’s just music, so you can play it with the mute button on).
In short, the two numbers match compass directions and are closely linked to a shifting magnetic north, which is why they occasionally get changed. There are some other interesting tidbits in the video, like how the difference between the two numbers is always 18 (so if there are two runways and one is 30, the other would be 12). The first number uses the actual compass bearing rounded to the nearest 10 degrees and the last number is always dropped. The other number is the opposite direction on the compass. Big airports (like Chicago’s O’Hare) may have parallel runways with the same numbers but these then would get an L, C or R after the number for “Left,” “Center,” or “Right.”
Good stuff, right? For more on the numbers on runways, watch the video.