The idea is simple and it requires only 35 units, but it needs from 2 to 6 hours approximately to be implemented with charting properly.
1. Make a list with all the roulette numbers
2. Each time a new number comes strike it off with a line
3. When only 2 numbers have left to show up, then bet all the rest 35 numbers for only once
4. Since you won restart from scratch, never bet twice or more against the 2 long sleepers!
The charting has to restart with clean slates!
Since the betting is not frequent and the potential profit only 1 unit I recommend to use 25 Euros or $ worth of chips, or more.