Eine Einführung in

Oracle  
We can use modular arithmetic to calculate the day of the week. We happen to know that 20 May 1962 was a Sunday. We calculate the number of days from that day and take mod 7 value. This tells us the day of the week: 0 is Sunday, 1 is Monday...  
Specific to Oracle  
Dates may be subtracted. The answer is in units of days. 