Arrays in Ada start at the index based on the index type of the array. You can even use an enumeration type as the index:

    type Day is (Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday);
    type Hours is array (Day range <>) of Natural;

    V : Hours (Monday .. Friday);

Which index type you should use depends on the problem that you're trying to model. You can find out the lower/higher end of a type/variable with the 'First and 'Last attributes.

IIRC there's an RFC though to force the lower end of the index to a certain value like 1 or any other number/enum.