GDOUTL 

     GDOUTL is the output vertical level in the target vertical
     coordinate.  The value of GDOUTL is stored for identification
     and access purposes with the output grid; it is not used in
     the vertical interpolation itself.  To specify the level to
     which to interpolate, use DESIRE.

     DESIRE and GDOUTL are specified separately because GEMPAK requires
     vertical levels in grid files to be integers.  For example, by
     convention, for the PV surface PV = 1.5 PVU, an output grid level
     of 0.0000015 is not allowed.  By convention, one could specify
     this level as GDOUTL = 15, and DESIRE should still be = 0.0000015.