Many people like to bet on the most recent numbers that have come up. For instance they might bet on the last 7 unique numbers and continue to bet on them while adding the most recent number with each turn.
This is based on what some call the rule of thirds. Basically in 38 a turns of a an american roulette wheel (37 for a european) it is practically impossible to have 38 unique numbers. If most of the time there will be 24 unique numbers and 12 repeaters - some of them will appear more than once.
If you want to try this system you will need to work out how to raise the amount bet so as to have a profit when you finally hit.
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