A very simple and effective inside bet.

Divide the numbers into 4 groups of Red&Black

Black:


A) 2,4,6,8
B) 11,13,15,17
C) 20,22,24,26
D) 29,31,33,35

Red


A) 3,5,7,9
B) 12,14,16,18
C) 21,23,25,27
D) 30,32,34,36

Trigger: Whenever 2 groups have been recently hit, bet the 2 unhit groups.

Progression: 8 numbers = 1.1.1.1.2.2.3.4.5.6.8.10.13.17.22.