[notinty]

It's 0.001; the first 2 9's count.

  5N  = 99.999%
  3N  = 99.9%
  1N5 = 95%

5N is <43m12s downtime per month.

[1-6]

I considered writing it as a percent but then decided against using it and moving the decimal instead. But good info for clarification.