R. I. Nelson wrote:
> You have the margins set with a tolerance of  +-0.0005".
> You have the tools to read to 0.00005".  You have apart that is
> supposed to be 1" DIA.  It measures  1.0000" with calibrated mics any
> one with common sense can call that a 0 tolerance part.

No that's not common sense, just plain wrong.

What you are really saying is that the tolerance is below the level you care
about.  That's fine, and deciding what the level needs to be is part of
enginnering, but you don't have and never can have 0 tolerance.

There's enough public misundertanding about this concept that it's important
(in fact irresponsible not to) for us engineers and scientists to state it
correctly.  This sort of erroneous statement and imprecise use of terms
needs to be squashed whenever possible to avoid even more confusion and
misunderstanding by non-technical people.

Lest you think this is just theoretical agument, consider that
misunderstanding of this issue almost caused bad public policy.  Politicians
are fond of saying they support a "zero tolerance" to drugs.  A few years
back when this was codified into law, the original wording literally set the
acceptable level of drugs found at zero.  For example, the Coast Guard would
have been able to sieze your boat for finding any drugs at all.  Can you
guarantee that there are no opiate molecules on your boat?  Nobody ate a
poppy seed bun 2 years ago and dropped a seed?  If you set the level at
zero, then you are really setting it at whatever the tolerance of the
equipment on hand is to detect it.  This can vary widely making the
application of the law unfair, and it also changes over time as equipment
gets more and more sensitive.  I believe the law was eventually modified to
spell out a specific quantity before it was passed.

I'm sure there are other examples where this misunderstanding has caused
real harm.

So please, do yourself and everyone else a favor and stop making rediculous
claims of "0 tolerance" parts.  Since you're presumably a technical person
on this list you really should know better.


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