That hunk of metal to the right is the world's most accurate clock, say people with more knowledge of time and atomic clocks than anyone else.
Called a cesium fountain clock (aka atomic clock), this British ticker is accurate to within two 10 million billionths of a second and won't lose a second for the next ten million years or more. I hope someone is around to wind it at that time, otherwise things could get awkward when our bioconstruct kin are zipping around with their FTL drives and arrive in Alpha Centauri a full second late.
Back on Earth, on our side of the pond, the National Institute of Standards and Technology has the NIST-F1 cesium fountain clock, which last reported an accuracy/uncertainty of 3 x 10-16. That's about 100 million years between losing or gaining a second to the layman. I'll take one for my wrist, please. [CNET]