This command returns an integer from 1 through 7 which shows what day of the week it was on a certain date. The Ti-89 Titanium manual says that this function may not give accurate results for years prior to 1583 (pre-Gregorian calendar).
|Integer value:||Day of the week:|
:dayOfWk(1948,9,6) : 2 :dayOfWk(1600,1,15) : 7
The above examples find that September 6th,1948 was a Monday, and that January 15th, 1600 was a Saturday. It also works with future dates, in case you want to use that in a program.