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Re: [Phys-l] Significant figures -- again



Despite having read John Denker's reasons for feeling as he does about "sig figs," his position continues to mystify me. Obviously it is true that "sig figs" are not a substitute for uncertainties. On the other hand, I have only one of two possible reactions when someone quotes a length as "3.8675309 cm":

1) He or she is referring to an EXTREMELY precisely determined length.

or

2) He or she is demonstrating his or her numerical ignorance.

I see no reason whatsoever not to expect people (including students) to express numerical data using an appropriate number of digits. It's simply a matter of using proper "numerical grammar." There may be no "right number of digits," but there are most certainly "wrong numbers of digits." I wouldn't and don't waste any time on "the rules for sig figs" and I would never penalize a student for using, say 2 or 4 digits to express a number that "the rules" would say should have 3, but I will continue to penalize them for using, say 1 digit or 6 or more in such a case.

John Mallinckrodt
Cal Poly Pomona

On Mar 12, 2012, at 10:34 AM, John Denker wrote:

I still think it is a Bad Idea to endorse -- explicitly or implicitly --
the idea that the number of digits tells you anything about the
uncertainty, tolerance, significance, or anything else.

Cutting a board to 3.8675309 ± 0.5 cm is not particularly difficult.
Cutting a board to 3.8675309 ± 0.0000005 cm is quite a bit more difficult.