1	-5      12-13	+1	24-25	+7      
2-3	-4      14-15	+2	26-27   +8
4-5	-3      16-17	+3 	28-29	+9
6-7	-2      18-19	+4	30-31	+10
8-9	-1      20-21	+5	etc.
10-11	 0      22-23	+6