Quality metrics

Sometimes you'll hear that a process has so many nines of reliability or that the error rate is so many sigmas. A few years ago I wrote a post on converting between nines and sigmas. See that post for details, approximations, etc.

Here I'd like to post a new graph that I believe is an improvement on the graph in the original post.

The grid lines make it easier to see how to convert between nines and sigmas. For example, 5 nines corresponds to a little more than 4 sigmas.

It's curious that 3 nines is approximately 3 sigmas, and 9 nines is very nearly 6 sigmas. There are no more points on the red curve with near integer coordinates until you go out to 72 nines, which is nearly 18 sigmas.

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