It is not a big surprise that any roulette wheel is mechanical by its design. As opposed to slots that are controlled by special microprocessors, the wheels of roulette are constructed of wood, metal and synthetics enduring tear and wear over time. Here inconsistency is developed when the roulette wheel spins. Thus, it slightly begins to tilt and as a result causes the bias of roulette wheel.
The biased wheels usually can be exposed by roulette players that track down such things. Those are used to examine a wheel for incredible number of spins. Then wheel attackers can emphasize tendencies of particular roulette and apply this knowledge in order to improve their gaming odds. For instance, one barely perceptible tilt can increase the probability of particular numbers on which the ball will land. Naturally a roulette player modifies his betting strategy and takes an advantage of existing tendency.
Frankly speaking, it's hard to find biased roulette wheels at land-based casinos today. The owners recognize the possible losses and provide their roulettes with frequent technical checkup and testing. Moreover, you cannot expect to come across the roulette bias playing at online casino.
In due course such type of wheel was used during incredible scam in Monte Carlo provided by Charles Jagger and his team. They walked away from casino with amazingly large amount for that time - $300,000.