WIZ - Reliability indexes - page 1

All ZOZ objects have a "Reliability Index" or "RI". It measures the probability that the object will not fail (by crashes, fires, or world-ending cataclysms). Of course, this measure is only an estimate -- but it has its usefulness. It is defined as:

   RI = -log10(probability of a failure in the next one hour).

It can also be loosely thought of as "number of zeros" when expressed as "1 in a thousand" (1000 = 3 zeros, RI=3), or "1 in a million" (6 zeros, RI=6).

It can also be thought of as the number of "9"s in the probability that something does NOT fail. EG, if the probability of failure (in the next hour) is 1 in a thousand, that is a 99.9% probabily of not failing, and that is 3 nines, RI=3.

Here is a small table of RIs and their corresponding probabilities:

   Probability of failure             Probability of not failing   RI
   ----------------------------       --------------------------   --
   1 in a hundred  =  0.01            99%                           2
   1 in a thousand =  0.001           99.9%                         3
   1 in a million  =  0.000001        99.9999%                      6
   1 in a billion  =  0.000000001     99.9999999%                   9
   1 in a trillion =  0.000000000001  99.9999999999%               12

There is little point in an RI greater than 12. A trillion hours = 114 million years. If something fails after that, I don't think anybody will care.