Many systems only bet on numbers once they have repeated a few times but what happens if those numbers don’t repeat. You will be losing money as many numbers will repeat a couple of times then go unseen for a long period of time.
A player must learn how differentiate between those that go unseen and the repeaters. Since we cannot really foresee which numbers will repeat and which ones will go unseen for longer periods of time we will need to bet on those that have been called for at least 20 spin then they should repeat.
This is what occurs on a roulette table most of the time. The numbers will go unseen and once they hit they will be active for a time frame and then goes back to being unseen again. The best strategy is to write down each number as they hit and the ones that don’t come up for at least 20 spins and bet a single chip on one of those numbers. If you hit place another bet on it but if for some reason that specific number doesn’t hit for another 8 – 10 spins you will need to move onto another number.