STOPL 

     STOPL is the level in the input data file at which to end the
     search for the output vertical level in gdpvsf.  STOPL must be
     a specific grid level in the input data file.  The search may 
     proceed upward or downward, depending on the relative locations of
     STARTL and STOPL.

     If the desired level in the new vertical coordinate is not 
     encountered in a particular grid column between STARTL and STOPL,
     the value of all interpolated fields in the output file will be 
     set to missing at that grid point.