Here’s a fascinating video about the difficulty in measuring the earth, beginning with the idea that the Prime Meridian, famously running through Greenwich, UK, is actually about a hundred meters off. Or it’s not. It all depends on who is measuring, and where.
Warning: This guy covers an amazingly wide range of fascinating topics. If you’re at all the curious type, you’ll get sucked down a rabbit hole within minutes, and you may never get back out. You have been warned.