RE: doing date arithmetic in CL(and how close is good enough)

Agreed.  I did say "pretty darned good."  Nearly 4000 years of accuracy is
nothing to sneeze at.  Whole calendar mess is a discrete approximation of
continuous stuff.  Tidal friction and some other things I can't remember or
never learned about make the relationship between year and day length a
moving target.    

BTW, Newtonian mechanics works real well for sizes above the quantum level
and velocities that aren't too close to the speed of light.  The real scary
thing is that Ptolemaic astronomy works pretty well for predicting the
positions of stars and planets if you keep making little changes in the
epicycles and so forth.  

> -----Original Message-----
> From: Shaw, David [mailto:dshaw@spartan.com]
> Sent: Tuesday, January 11, 2000 10:25 AM
> To: 'RPG400-L@midrange.com'
> Subject: RE: doing date arithmetic in CL
> 
> 
> -----Original Message-----
> From: Joel Fritz [mailto:JFritz@sharperimage.com]
> 
> I agree with you about date calculations in CL and the new 
> Y2K myth, but in
> all fairness, I think a lot of engineering calculations are based on
> algorithms that work most of the time or at least produce 
> results that are
> "close enough."  e.g. Newtonian mechanics. The leap year 
> algorithm that uses
> 4, 100, and 400 is only a pretty darned good approximation, 
> admittedly a lot
> better than the one that only uses 4.
> 
> I had an extra day off and need to slough off some of the extra energy
> through pedantry. <g>
> 
> ---------------------
> 
> Joel,
> 
> Well, if we're going to be pedantic, let's pick a nit: the 4, 
> 100, 400 rule is
> exact for the Gregorian calendar for the range from AD 1 to 
> AD 3999.  The
> Gregorian calendar is where the approximation exists - it 
> attempts to maintain
> its anchor point in approximately the same part of the 
> earth's orbit around the
> sun from year to year.
> 
> Oh, that AD 3999 thing?  Some astronomers say that to 
> maintain the approximation
> years divisible by 4,000 should not be leap years, unless 
> they are divisible by
> 20,000.  I've never been able to verify whether that is 
> "official" in the
> Gregorian calendar or not - I'm not even sure who would decide.
> 
> Dave Shaw
> +---
> 
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