Hmm, aren't Jan and Feb months 13 and 14 of the previous year?

On 8/4/06, Brooke Clarke <brooke@pacific.net> wrote:
>
> Hi:
>
> I almost have it working and found a problem while testing.  Here are
> some test dates and the results:
> 28 Feb 1992 Sat - 0 works
> 29 Feb 1992 Sun - 1 works
> 28 Feb 2000 Mon - 2 works
> 29 Feb 2000 Tue - 3 works
> 1 Mar 2000 Wed - 4 works
> 28 Feb 2004 Sat - shows Sun 1
> 29 Feb 2004 Sun - shows Mon 2
>
> When manually calculated as follows 28 Feb 2004 comes out Sunday.  What
> am I doing wrong?
>
> Zeller year for Feb 2004 is 03 (-1 because month is Feb)
> Zeller Month number is 12 (Jan & Feb are month # 11 & 12 of prior year
> so Feb 29 falls at year end)
> Zeller Century is 6 (i.e. 20MOD7)
> Zeller Day of Month is 0 (i.e. 28MOD7=0)
> Zeller DOW = Z_DOM + 13*(Z_month+1)/5 + Z_Year + Z_Year/4 + Z_Century/4
> + 5*Z_Century
>            =   0   +  5 (33MOD7)      +  3     +   0      +     5
> + 2 (100MOD7)
>            = 1 (15MOD7) = Sunday
>
> Have Fun,
>
> Brooke Clarke
>
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