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platinum-iridium

   same category are measured.  Usage: silly.  The notion is that one
   of whatever it is has actually been cast in platinum-iridium alloy
   and placed in the vault beside the Standard Kilogram at the
   International Bureau of Weights and Measures near Paris.  (From
   1889 to 1960, the meter was defined to be the distance between two
   scratches in a platinum-iridium bar kept in that same vault --- this
   replaced an earlier definition as 10^(-7) times the distance
   between the North Pole and the Equator along a meridian through
   Paris; unfortunately, this had been based on an inexact value of
   the circumference of the Earth.  From 1960 to 1984 it was defined
   to be 1650763.73 wavelengths of the orange-red line of krypton-86
   propagating in a vacuum.  It is now defined as the length of the
   path traveled by light in a vacuum in the time interval of
   1/299,792,458 of a second.  The kilogram is now the only unit of
   measure officially defined in terms of a unique artifact.)  "This
   garbage-collection algorithm has been tested against the
   platinum-iridium cons cell in Paris."  Compare golden.