"Stan Prevost" wrote in message
...

Where does the 1000 come from?


From FAR 91.155(c).


§ 91.155 Basic VFR weather minimums.

(c) Except as provided in §91.157, no person may operate an aircraft beneath
the ceiling under VFR within the lateral boundaries of controlled airspace
designated to the surface for an airport when the ceiling is less than 1,000
feet.