Re: Sig Figures

["William J. Larson" <bill_larson@CSI.COM>]

With great trepidation I contradict Leigh.
OK my triple-layered Kevlar body armor is on.  :-)

Errors should be added in "quadrature" i.e. as the square root
of the sum of the squares. Leigh's method over estimates
the total error because both (all) of the errors are unlikely to
be at their biggest (or smallest) extremes simultaneously.

Incidentally I'm SURE Leigh knows this.

Cheers,
Bill Larson
Geneva, Switzerland



----- Original Message -----
From: Leigh Palmer <palmer@SFU.CA>
To: <PHYS-L@lists.nau.edu>
Sent: 2000 January 31 11:02 PM
Subject: Re: Sig Figures


> > When your dealing with angles in problems like vector addition, or
> > inelastic collision at vector angles, how do you handle angles and
> > significant figures?  The book I use tends to keeps the angle to about 2
> > decimal places and does not follow significant figures of the data.
> > What are the guidelines for this?
>
> Don't use significant figures. Instead you should insert uncertainties
> in your inputs of the magnitude of uncertainties in your measurements.
> Calculating your result two more times (using the extreme uncertainties)
> will answer your question for you. Given that you probably use a digital
> calculator this should not be an excessively arduous task.
>
> "Significant figures" is a schoolboy rule; it isn't used in science
> because it is so often wrong. I don't even teach it; I do carp about
> *insignificant* figures, however.
>
> Leigh