           
        2     =     /150     
         
                                                 
     ~                        1/24~1/12
    1~2                                       1/8
       2~4                                        1/6
       4~6                                        1/4                  
       6~8                                        1/3
       8~12                                      1/ 2           
       12~15                                    3/5
       15~18                                    3/4