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[Phys-L] Re: infinite sig. figs.



John D said:
=20
I don't understand any of what has been said about rounding off
"immediately prior to reporting" as opposed to rounding off
intermediate results.

That seems like just a corollary of your own rules.=20
The proper roundoff rules are:
-- keep many enough digits to avoid unintended loss of
precision.
-- keep few enough digits to be reasonably convenient.

With a calculator, it is reasonably convenient to keep 8+ digits inte=
rnally for any intermediate results. Thus there is no real point in =
rounding off, since any number of digits your calculator provides are=
convenient. OTOH, typing a long set of digits into a "summary" of t=
he calculations becomes inconvenient. You can easily drop a few digi=
ts without any unintended loss of precision.


If it is OK to throw away the guard digits because the result
will never be used, why not skip doing the report entirely,
since the result will never be used?

I don't see the rationale that every report must be as precise as hum=
anly possible or it is useless, which seems to be what you are saying=
. For example, from today's news: "In all, nearly 2 million people a=
long the Texas and Louisiana coasts were urged to get out of the way =
of Rita, a 400-mile-wide storm that weakened Thursday from a top-of-t=
he-scale Category 5 hurricane to a Category 4 as it swirled across th=
e Gulf of Mexico." The numbers reported here have thrown out all sor=
ts of guard digits and precision, but these reports from NOAA and the=
news media are being used extensively to inform people of the situat=
ion.


Tim F
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