Why a kg is currently my favorite SI unit:
-A meter is defined as the length light travels in a vacuum in 1/299,792,458 of a second
-A second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the caesium-33 atom.
-A kilogram is defined by this cylinder of platinum-iridium alloy kept in a vault near Paris. Science!
Picture taken by the National Bureau of Standards
Source: physicsphiends
