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



On 04/12/2012 04:12 PM, John Mallinckrodt wrote:
John Denker and I obviously come down on different sides of the
question of whether or not there exists even a single problem which

1) has an answer that would and should be positively embarrassing to
quote to 10 or more digits

AND

2) is NOT merely an "ivory-tower busywork assignment, where the
answer will not be used for any practical purpose, but instead will
simply be checked for compliance with artificial, nonsensical rules.

In support of my contention that there MOST certainly are, I would
submit every worthy Fermi question ever asked.

Are we going to play lawyer games now? I'd rather not, but if you
insist .....

Does anybody on this list really think I *always* write 10 or more
digits?

Does anybody on this list really think there are only two possibilities,
namely (a) always writing 10 or more digits, or (b) never doing so?

As I see it, the gauntlet was thrown down on 03/12/2012 12:49 PM,

He or she is demonstrating his or her numerical ignorance.
....
I will continue to penalize [students] for using, say 1
digit or 6 or more in such a case.

Then again on 03/12/2012 05:10 PM we have:

I'd be utterly flabbergasted to hear you quote a length as 3.8675309
cm if you only knew it to within a few mm.

which also seems quite categorical and uncompromising.

I disagree with this extreme position, for quantitative numerical
reasons that I have explained in detail. That does not mean that
I am arguing for the opposite extreme position. I am not saying
that we always need to use 10 digits or 20 digits or more ... but
rather that we *sometimes* do ... and when we do, it does demonstrate
"numerical ignorance".

================

Oh, and while we are playing games, are Fermi problems really where
you want to pitch your tent? That is, are you going to argue that
sig figs are appropriate for Fermi problems? Pray tell, how many
sig figs do you use to express a quantity that is uncertain by an
order of magnitude in either direction?

There's a lot more I could say about this, but I forbear.

See also http://www.av8n.com/physics/uncertainty.htm
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