The days of a "fixed" kilogram seem to be numbered, with moves afoot to set our SI unites based on fundamental constants. Reddit discussion: http://redd.it/2etf3o Extra from this video: http://youtu.be/XvZGpKQCzzo Standard weights: http://youtu.be/yGfCp7CPx-M Replica of the Parisian kilogram: http://youtu.be/h4XIOpKWc1Y Derek holds a kilo-ball: http://youtu.be/ZMByI4s-D-Y This video features Professor Michael Merrifield: https://twitter.com/ProfMike_M Visit our website at http://www.sixtysymbols.com/ We're on Facebook at http://www.facebook.com/sixtysymbols And Twitter at http://twitter.com/#!/periodicvideos This project features scientists from The University of Nottingham http://bit.ly/NottsPhysics Sixty Symbols videos by Brady Haran A run-down of Brady's channels: http://bit.ly/bradychannels