"five nines": purity (1961), reliability (1992)

Mark A. Mandel mamandel at LDC.UPENN.EDU
Mon Apr 11 00:13:29 UTC 2005

Benjamin Zimmer writes:

Shafer is extending the expression "five nines" -- referring to a goal of
99.999% reliability -- from its usual context of networking or
telecommunications systems.  One article ("Reality Check On Five-Nines"
<http://www.bcr.com/bcrmag/2002/05/p22.php>) claims that "everyone in
telecom has been using the term 'five-nines' for decades."  I can find
"five nines" back to 1961 in references to chemical purity, but only to
1992 in references to reliability.

While I can't give a citation, I feel quite sure* that I saw this and
comparable expressions (of the form "n nines") used long before the nineties
in science fiction to refer to degrees of probability or certainty.

-- Mark A. Mandel
[This text prepared with Dragon NaturallySpeaking.]
*at least two nines

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