Re: NEC-LIST: Accuracy vs precision

Yes; the 3.452546 number for Pi being akin to the highly precise and repeatable (but
inaccurate) 3.518 dB once measured for a coax connection without the center-
conductor bullet installed, as mentioned.

Another common misteak is when an obviously rough number like 1 000 000 km distance
(of a spacecraft from Earth example) is precisely converted to miles as 621 371 while the
intent was to suggest something like 620 000, or even more likely, 600 000 miles.

Precision vs accuracy confusions can cause serious misunderstandings of otherwise
good metrology work. Interestingly, precision can be rigorously determined using many
identical measurements and then looking at the simple stats to get an estimate of the
*random* error. But accuracy is, among other things, usually dependent on some
indeterminant errors (bias, offset or 'systematic' types) and (Quote) "......must be estimated
by common sense, or what perhaps more candidly should be called guesswork". (Quote
from the Preface to the second edition, Theory of Error, Yardley Beers, Addison-Wesley
1957). Beers was with National Bureau of Standards, Radio Standards Division, Boulder
CO. His little 65 page softcover monograph is an enduring masterpiece.

As succinctly as is possible, I think, Beers says "If an experiment has small *random* errors
it is said to have high *precision*. If an experiment has small *systematic* errors it is said
to have high *accuracy*.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

At 02:27 PM 1/13/2003 +0000, you wrote:
>Dan
>Thanks for your comments and the dictionaries I looked up define 'accuracy'
>as 'conforming to a standard or to truth' while 'precision' seems to be more
>concerned with the number of decimal places quoted: the New Penguin
>Dictionary of Science says that to state that pi is equal to 3.452546 would
>be precise but significantly inaccurate. So accuracy is worth having,
>precision on its own is not - does that agree accurately with your
>remarks?
>Alan
>
>
>
>
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Dan Bathker

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