I think:
    that the first decade consisted of the years  I - X,
    that the first century consisted of the years I - C,
and that the first millenium consisted of the years I - M
(everything A.D and in Roman notation).  Thus my new sig file:
Hans Dinsen-Hansen    http://www.danbbs.dk/~dino/
                      mailto:dino@danbbs.dk
If Jan. 1st 2000 is the start of a new millennium:
   - Which millenium had 999 years?
   - i.e. which century had 99 years?
   - i.e. which decade had 9 years?