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Re: [Phys-l] New gravitational constant



John Denker wrote:
(6.67259 +/- 0.001) * 10^(-11) m^3kg^(-1)s^(-2)
If this is
the way CODATA reported their previous value
(5 places after the decimal with an uncertainty in the
third place after the decimal) then they've not learned
basic rules of reporting uncertainties that I drum into my
students! :)

Maybe it would help to do more thinking and less drumming.
The CODATA team is comprised of the world's leading
metrologists. It might be worth considering the possibility
that they know what they're doing.

In fact there are exceedingly good reasons for reporting data
such that the uncertainty is dozens of times greater than one
count in the last decimal place.

The "significant figures" rules you learned in high school are
completely unacceptable for serious work, for reasons explained
in detail at:
http://www.av8n.com/physics/uncertainty.htm

Perhaps it would be advisable to allow that someone posting
on this might know a little about statistical analysis also,
beyond the high school level. Your tone is pretty arrogant
and not appreciated in the least.

My complaint about reporting a number like what was
quoted above, 6.67259 +/- 0.001 still stands, and was based
not on "what I was taught in high school", but on years of
reporting results of precision measurements made by me and
colleagues. I'm no idiot that just fell off the turnip truck, but
someone who regularly uses and reports the results of such
averaging in his research.

I repeat that the numbers reported must mean something ... if the
central value of the average they are quoting is good to
that degree, 6.67259, then would you care to comment on
the significance or utility of quoting those last two decimal
places when the uncertainty is in the 3rd place after the decimal?
How can the existence of the .00059 mean anything if the
result is essentially 6.673 +/- 0.001? If they want to report those
digits, fine ... but they don't mean very much if you actually want
to USE properly the number they report.

My point is not that you can't calculate an average value that
has a result going out to the fifth point after the decimal - I'm
sure there's just cause for those digits. However, if I'm trying
actually to use the value of G they've reported, there's little
point in my going that far out... as the uncertainty dictates how
much I can trust that central value.

Todd Pedlar

--
________________________________________________________________________________
Todd K. Pedlar
Assistant Professor of Physics
Luther College
pedlto01@luther.edu
_________________________________________________________________________________