Date: Thu, 9 Dec 1999 17:14:42 +0000
Reply-To: John Whittington <John.W@MEDISCIENCE.CO.UK>
Sender: "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From: John Whittington <John.W@MEDISCIENCE.CO.UK>
Subject: Re: When large number of significant digits may be requir
In-Reply-To: <199912091405.OAA23544@vicar.netnames.net>
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At 09:01 09/12/99 -0500, HEATONE wrote:
> I did do well in my physics and chemistry classes (fairly advanced in the
>chemistry classes) and I was taught just the opposite, that you always use
all
>the precision that you have available until all the calculations are
completed.
>Then, you report the result to the precision of the least precise of your
>measurements. :-)
Indeed, and that's essentially what I described early in this thread - the
most important things being that (a) rounding is only done once and (b)
that it should generally be done 'at the end', after any/all computations.
However, I think we need to examine what is meant by using 'all the
precision that is available' during those earlier steps. If an instrument
or measurement produces a ludicrous degrees of significant figure (maybe
just because it happens to have 'a 12-digit display'!) in relation to the
actual precision of the measurement, then many of these 'significant
digits' probably do not come within the definition of 'the precision
available' - and are probably therefore best 'dropped' at the very start.
If all one is 'dropping' at the start is a pile of essentially 'random
numbers', then that should not have any impact on what follows.
That's how I see it, anyway!
Regards,
John
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