procedure TForm1.Button3Click(Sender: TObject);
var s:string;
Field: TFloatField;
f:tfield;
begin
Table.Close;
Table.Open;
//Field:= Table.Fields['POINT_Y'];
Field:=TFloatField.Create(Table);
//f := Table.FieldByName('POINT_Y');
f:=Table.Fields.FieldByName('POINT_Y');
Field.Assign(f);
Table.FieldDefs.Add('Depth', ftFloat, 20, false);
//Table.Fields.Add(Field);
end;