Uses: Tones only, Follows symmetry
Rule: Finds the median note(s) of the last value.

           ---c---
           c-f-g-c
              !
      !<<<<<<< >>>>>>>!
-C-Em-F-G-Am-C-C-Dm-F-G-Bm-C
              !
     C-Dm-Em-F-G-Am-Bm-C 

Inteval map

             ---1---
             1-4-5-1
                !
          !<<<<< >>>>>!
    -1-3-4-5-6-1 1-2-4-5-7-1
                !
         1-2-3-4-5-6-7-1