Please HELP finding center of surfaves

[Bradip Pitt]

Hello everybody, I'm a novice user of AUTOCAD and I'm starting learning about AUTOLISP and Autocad customization...I'm lookin for an AUTOLISP routine which can find the centre of a selected surface and possibly place a reference system, as much as possible (depending on the congiuration of the surface) parallel to the fixed one, in that point.

Will apreciate very much every kind of help

Alberto (preparing his mechanical engineering final thesis)