I love it! Thanks, John, for speaking out. I've vehemently fought for years
to have the evil sig figs dropped from Chem and Physics curriculum
(curriculae?). I did a summer intern thing at Princeton Plasma Physics Lab
and the real scientists, for the most part, never even heard of them. They
dropped the term 'tolerance' quite a bit when discussing their numbers and
measurements. In other words, "How far off can my number be and still work?"
Daryl L. Taylor, Fizzix Guy
Greenwich HS, CT
PAEMST '96
International Internet Educator of the Year '03
NASA SEU Educator Ambassador
www.DarylScience.com
This email prepared and transmitted using 100% recycled electrons!
-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu] On
Behalf Of John Denker
Sent: Wednesday, August 10, 2005 12:40 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: fall cleanup: sig figs
A message from the SPCD (Society for the Prevention of Cruelty to Data):
Every September, in classrooms all over the country, kids are taught about
"significant figures".
This has got to stop. The notion of "sig figs" is garbage. If you see a
number such as 2.54 in isolation, you cannot know whether it has 10%
uncertainty, 1% uncertainty, or no uncertainty at all.
Different texts tout wildly inconsistent versions of the "rules"
for using sig figs.
People who care about their data don't use sig figs at all; they state the
number and its uncertainty separately, explicitly, as in
1.672 621 71(29) e-27 kg
Let's be clear: Uncertainty needs to be expressed. It doesn't need to be
expressed using the method of "sig figs".
Uncertainty is not the same as significance. A number that has uncertainty
at the .01 level may be significant at the .001 level, for instance if there
is signal-averaging going on.
Roundoff is not the same as uncertainty or significance. The proper
roundoff rules are:
-- keep many enough digits to avoid unintended loss of
precision.
-- keep few enough digits to be reasonably convenient.
In particular, rounding things off in accordance with the usual "sig figs"
rules commonly results in disastrous loss of precision. Don't do it.