|                  |   |    +----6--------->   
 |                  |   |    |  +--4-------->    
 |                  |   |    |  |          |     
 |                  |   |    |  X  X  X  X |     
 |                  |   |    X  X  X  X  X |
 +12-11-10--9--8--7-------6--5--4--3--2--1-+