[time-nuts] Rubidium standard

[Mike S]

At 05:22 AM 11/18/2009, Steve Rooke wrote...
>The point I should have made is that most quoted MTBF figures have a
>reasonable bearing on the lifetime of the item,

But your point would then be almost perfectly incorrect. MTBFs are not 
meant to, nor do they, predict product lifetimes. They are 
measures/predictions of product reliability.

"What does MTBF have to do with lifetime?  Nothing at all!" - 
http://www.ece.cmu.edu/~ganger/ece546.spring02/readings/mtbf.description

"MTBF represents the statistical approximation of how long a number of 
units should operate before a failure can be expected. It is expressed 
in hours and does not represent how long the unit will last." - Learn 
(or review) the difference between MTBF and lifetime, Control 
Engineering, 9/24/2008; 
http://www.controleng.com/article/312365-Learn_or_review_the_difference_between_MTBF_and_lifetime.php

I don't grant Wikipedia strong authority, but it is useful, and has 
this to say: "MTBF is commonly confused with a component's useful life, 
even though the two concepts are not related in any way. For example a 
battery may have a useful life of four hours, and an MTBF of 100,000 
hours. These figures indicate that in a population of 100,000 
batteries, there will be approximately one battery failure every hour 
during a single battery's four-hour life span."

There's much more out there, if you make the effort.

>I felt that an example based on humans was not really applicable to
>the real world of electronic items but that is my own opinion and I'm
>happy if you disagree with me.

MTBFs are not exclusive to electronics. Statistics, math and MTBFs are 
objective matters, so your opinion really doesn't make any difference.