UPDATE. Having checked with the embassy, it appears that they have used the number I put in the form as "intended days of stay" that I have calculated to 9 + 2 = 11 days as any hotel stay or car rental would do, namely simply subtracting the numbers. Never on earth could I think they put it as the hard day limit inside the visa, leaving me with no flexibility and literally putting me at risk to become "illegal" with any small disruption.
When applying for an Italian (Schengen) visa, I have declared trips to Italy from September 2 to 11 and from September 30 to October 2, and have received the multiple type C schengen visa but only for 11 days! Which presumes they have calculated 9 + 2 for the trips I declared.
However, the site http://www.schengen-calculator.com/ calculates both entry and exit days, so for the above dates as declared I would get 10 + 3 = 13 days, which would make their calculation wrong.
But that site only refers to the 90 days visa. It does not let me enter the 11 days C visa. So their calculation is different for that visa?
Is there any reliable site giving clear information about how precisely the days are calculated, that I can use in my case?