I think that the problem here is that some people are defining
"handspan" to mean the width or length of one's hand and others, I
think, may be referring to the maximum distance from finger-tip to
finger-tip with arms held wide open.

Sean


On Sat, Jul 18, 2009 at 3:28 PM, Olin Lathrop<olin_piclist@embedinc.com> wr=
ote:
> Alan B. Pearce wrote:
>> I believe that 5 decimal places is enough to calculate the
>> circumference of the earth to within a handspan. Sorry don't have a
>> reference, I just remember being told it at one stage.
>
> That's easy enough to check. =A0The circumference of the earth is about 2=
5,000
> miles =3D 132,000,000 feet =3D 1,584,000,000 inches. =A0Let's say your "h=
andspan"
> is a unit Palm, which is 4 inches. =A04/1,584,000,000 =3D 1/396,000,000 =
=3D
> 10**-8.6, so you need about 9 significant digits. =A0Sorry, 5 won't cut it
> unless you meant 5 digits right of the decimal point with another 4 to the
> left.
>
> We can also look at the reverse. =A0The best accuracy you can get with 5
> digits is 99,999. =A0With a implied error of +- 1/2, that is a error of
> 1/199,998. =A01,584,000,000 * 1/199,998 =3D 7920 inches =3D 660 feet =3D =
1/8 mile =3D
> 220 yards =3D about two soccer fields end to end.
>
>
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