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I have worked in a machine shop that was climate controlled Temp and 
humidity. if the climate went out of the control zone we would have to 
stop operations on some materials.

I know on the less critical stuff that I worked on we had Tolerances on 
every drawing   most of the stuff I did was + or - 0.0005".  but we 
still tried and usually achieved 0 tolerance.  our measuring tools were 
checked daily and we had gauge blocks to double check them.

That is why I say 18 pulses per second is ABOUT 55.55555ms. and not EXACT.


Gerhard Fiedler wrote:

>
>
>Mathematics (and logic) is the only thing that's exact, and it's neither
>science nor engineering. I'd go so far as to say that there's /nothing/
>exact in engineering (and that goes for every country I know :). Every
>measurement has a tolerance range around it, and not even that range is
>exact, as it's usually just a short hand notation for a not quite well
>known probability distribution around the given value.
>
>In science and engineering classes, IMO, should be taught that e.g. 6 V
>doesn't really say much, it needs to be e.g. (6 +-0.2) V to make sense.
>Because for example (6 +-0.00001) V is something quite different -- and
>even that's pretty close to "right on" or "exact" or "no variance", it's
>obviously none of these. I've never seen a measurement that was 6 V
>/exact/, in the sense of (6 +-0) V. And, you may find that ironic (but it's
>actually quite obvious), the more you get into high precision work, the
>more important become the tolerances. They are left out (and as such are
>implied to be low precision) only in low precision situations; everywhere
>precision is relevant they always use values with tolerances. 
>
>I don't know whether you have done engineering work for other people. One
>of the most common phrases one hears is "that's close enough" (or maybe
>"that's too expensive, make it simpler" :). We (almost) never do the best
>we could do given unlimited funds and time, we pretty much always do it
>"good enough" and "as simple/cheap/quick as possible". Nothing "exact" or
>"precise", all a matter of trade-offs, a lot of "half way things". Having a
>good feeling for the "right" trade-off is basically what engineering is
>about... :)
>
>Now I don't know much about the military. Maybe they operate in a different
>universe :)
>
>Gerhard
>
>  
>


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