The Real Greenwich Prime Meridian

Every year hundreds of thousands of tourists come to Greenwich to pay a visit to the Prime Meridian line. But only an observant visitor realizes that something is wrong...

The prime meridian in Greenwich dates back to 1851 when Sir George Airy established it. As a standard for navigation, it was widely accepted within a few decades, even though the French resisted and instead opted for the Paris meridian to become the line of reference. But thanks to the International Meridian Conference in 1884, Paris was told to take a backseat to this one, true meridian. Unfortunately it's not quite as perfect as it seems. 

With the introduction of satellite based GPS navigation, the position of the Greenwich meridian that dated back centuries, and had been drawing visitors who wanted to straddle the line, was called into question. Modern instruments pointed out that, due to inaccuracies in the instruments used at the time the meridian line was established, it was marked 102 meters (334 feet) west of its actual position.

In terms of overall navigation, such an inaccuracy is a bit trivial. But this means that the tourists lining up for a picture at the Greenwich Observatory Monument could have saved some time and gone for a walk just a few hundred feet to the east in Greenwich Park for a picture at the real Greenwich Prime Meridian, which runs through an otherwise nondescript part of the park.