15.64.21  ELLIPSE 

This sets the default size for the major and semi-major ellipse sizes.  If
dy is omitted the ellipse becomes a circle.
SET ELLIPSE [SIZE=dx[,dy]] [PERMANENT]

PERMANENT - Makes the current setting the new default.
 
If  dx  is  omitted  it is set to the default.  If dy is omitted it is the
same as dx.