Nines (notation)

Their common uses include grading the purity of materials – especially precious metals and industrial gases – or measuring the availability of a service.

A percentage of 100% would, in theory, have an infinite number of nines – though, in the context of purity of materials, 100% is virtually unachievable.

The exact purity of very fine precious metals such as platinum, gold and silver can be of great interest.

[5] The purest gold ever achieved was reportedly produced at the Perth Mint in 1957, at "almost six nines" (99.9999%) purity, as measured by the Worshipful Company of Goldsmiths of London.

The purity of a gas is an indication of the ratio of it to other gases in its mixture, as measured by volume.

The purity of a gas is generally expressed as a grade prefixed with the letter N (rather than postfixed), indicating the "number of nines" in the percentage or decimal fraction.

[citation needed] Nines are used in a similar manner to describe computer system availability.