Type the following command in Unix shell. Of course, you can use it in $prompt or #prompt.
cal 9 1752
Surprised ???? That's the beauty lies in UNIX.
Isn't the output queer? A month with whole of eleven days missing. This was the time England shifted from Roman Julian Calendar to the Gregorian Calendar, and the king of England ordered those 11 days to be wiped off the face of the month of September of 1752. (What couldn't a King do in those days?!) And yes, the workers worked for 11 days less, but got paid for the entire 30 days. And that's how "Paid Leave" was born. Hail the King!!!