Constant Proportion strategy consists in betting a certain percentage of your bankroll on each spin of the roulette wheel. This means that the value of the bets will change, but their value when compared to your bankroll at the time will be constant. This gives the strategy its name.
The Constant Proportion strategy is very similar to the Constant Bet strategy but with an extra element. In the Constant Bet strategy, the bet values remain the same whether the game is going well for the player or if, on the other hand, it is going very badly. The Constant Proportion strategy, however, adjusts the bets according to previous results.
Thus, if a player is winning, the bets will increase in value, which would allow the player to win even more. However, if the player is losing money, then the value of the bets will slowly decrease meaning that the potential losses do not accumulate as quickly as with the Constant Betting strategy. It is this self-regulating mechanism that makes the Constant Proportion strategy better than the Constant Bet strategy.
For example, if the player bets 10% of his bankroll on a colour bet, and if he starts with a bankroll of €100, he will place a €10 bet on red. If he wins, then his bankroll will become €110, and the next bet will be €11. If he loses, he is left with €90 and will bet €9 on the following round. This will be the sequence of bets for the player, until he runs out of funds or chooses to stop playing, by employing the Constant Proportion strategy.
The Constant Proportion strategy tries to find a balance between:
High volatility - big wins possible, but also with high odds of losing everything quickly;
Low volatility - smaller wins possible, however, there is less chance (or no chance) to lose everything quickly.