tested this both live and rng with good results:
for the last three streets hit, bet the other two unhit numbers in those streets. that will be a six numbers bet
for an example (last spins)
3 numbers 1,2 would be bet
11 numbers 10,12 would be bet
28 numbers 29,30 would be bet
progression six numbers negative progression
1 1 1 1 1 2 2 2 3 3 4 5 6 7 8 10 12 14 17 21 25 30 36 43 52 62 74