Plot of High*Year.  Legend: A = 1 obs, B = 2 obs, etc.     
                                                                
 4000 +                                              A          
      |                                             A           
      |                                           AA            
 High |                                          A              
      |                                       A A               
      |                                        A                
 2000 +                                      A                  
      |                                     A                   
      |                                   AA                    
      |                AAAAAAAAAAAAAAAAAAA                      
      |        AAAAAAAA                                         
      |      AA                                                 
    0 +                                                         
      ---+---------+---------+---------+---------+---------+--  
       1950      1960      1970      1980      1990      2000   
                                                                
                                Year