The Jargon File (version 4.4.7, 29 Dec 2003):

platinum-iridium
 adj.

    Standard, against which all others of the 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. But this will have to
    change; in 2003 it was revealed that the reference kilogram has been
    shedding mass over time, and is down by 50 micrograms.) ?This
    garbage-collection algorithm has been tested against the platinum-iridium
    cons cell in Paris.? Compare golden.


The Free On-line Dictionary of Computing (30 December 2018):

platinum-iridium

    A standard, against which all others of the 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, as the bar defining the standard
   metre once was.

   "This garbage collection algorithm has been tested against
   the platinum-iridium cons cell in Paris."

   Compare golden.

   [Jargon File]

   (1997-02-20)