Why does "cal 9 1752" produce incorrect results?

[John Rowe]

It doesn't. (Sorry if you've already had dozens of versions of the
following posted).

   Under the old Julien calender, instituted by Julius Caeser no less,
there was a leap year every four years. I believe it was the Egyptians
who discovered this one because the seasons and the flooding of the Nile
were happening later every year.

It turned out this was slightly too many so the system was changed so
that years divisable by 100 are not leap years unless they are
divisable by 400 (eg 1900 wasn't, 2000 will be).  My dictionary says
this was done by Pope Gregory in 1582 but not adopted in England 'till
- you guessed it 1752 when people went to bed on Wednesday the 2nd of
September and got up on Thursday the 14th.

Incidently, as I recall there were great protests about this as people
thought they were losing 11 days of their lives. Plus, the Russians
being backward didn't do this which is why the October revolution
didn't happen in October, rather like the battle of Stalingrad which
happened in Volgagrad.

John

John Rowe
Exeter University Computational Physics group.
Exeter
England.