//input: DATE
//
// https://www.wikihow.it/Calcolare-il-Giorno-della-Settimana  (method 1)
//
MyDay, MyMonth, MyYear = CALL "UnpackDate"[MyDate]
IF MyMonth = 1 OR MyMonth = 10 THEN
   Mvalue = 0
ELSIF MyMonth = 4 OR MyMonth = 7 THEN
   Mvalue = 6
ELSIF MyMonth = 9 OR MyMonth = 12 THEN
   Mvalue = 5
ELSIF MyMonth = 5 THEN
   Mvalue = 1
ELSIF MyMonth = 6 THEN
   Mvalue = 4
ELSIF MyMonth = 8 THEN
   Mvalue = 2
ENDIF
d = MyDay + Mvalue
WHILE d > 6
   d = d - 7
WEND
y = MyYear MOD 100
Century = MyYear - y
Century = (Century MOD 400) / 100
IF Century = 1 THEN
   Century = 5
ELSIF Century = 2 THEN
   Century = 3
ELSIF Century = 3 THEN
   Century = 1
ENDIF
z = y
WHILE y > 27
   y = y - 28
WEND
y = y + round((z / 4) - 0.5) + Century
IF MyMonth < 3 THEN
   x = CALL "IsLeapYear"[MyYear]
   y = y - x
ENDIF
d = d + y
WHILE d > 6
   d = d - 7
WEND
IF d = 0 THEN
   d = 7
ENDIF
RETURN d - 1      //0=Sunday, 1=Monday...... 6=Saturday