Ok...it seems Christmas doesn't fall on a Tuesday every 90 years. So that's one theory that is false.
In this case, gong forward in time...you'd have to still use 1990/Tuesday as a starting point.
So when going forward we just reverse certain rules. Odd decades get 1 point and even decades get 2 points when going forward in time. When going backward odd get 2 and even get 1.
Count up the points in the same manner but as you go up the odd decades count as 1 and even count as 2 (reversed).
1990 = 1
2000 = 2
2010 = 1
2020 = 2
2030 = 1
total = 7 points
Now rewind from Tuesday 7 days and you get Tuesday.
2040 = tues
2041 = wed
2042 = thur
2043 = fri
2044 = sun
2045 = mon
So my error was not reversing the points for odd/even decades. :)
http://www.hf.rim.or.jp/~kaji/cal/cal.cgi?2045
In this case, gong forward in time...you'd have to still use 1990/Tuesday as a starting point.
So when going forward we just reverse certain rules. Odd decades get 1 point and even decades get 2 points when going forward in time. When going backward odd get 2 and even get 1.
Count up the points in the same manner but as you go up the odd decades count as 1 and even count as 2 (reversed).
1990 = 1
2000 = 2
2010 = 1
2020 = 2
2030 = 1
total = 7 points
Now rewind from Tuesday 7 days and you get Tuesday.
2040 = tues
2041 = wed
2042 = thur
2043 = fri
2044 = sun
2045 = mon
So my error was not reversing the points for odd/even decades. :)
http://www.hf.rim.or.jp/~kaji/cal/cal.cgi?2045