Jean le Rond d'Alembert (1717 – 1783) was a mathematician from France, who argued that that the probability of a coin landing heads increased for every time that it came up tails. From his theory, the betting system known as The D'Alembert System, evolved which consists of reducing the value of your bet on even money wagers the more you win and increasing your bet after losses.
The D'Alembert System is in a family of systems called The Progressions Systems, of which the more famous Martingale Roulette System is also a member.
D´Alembert is most usefully employed on even money bets on the roulette table, be that online or at a land based casino. It is best employed on a medium to long session, say 20 to 30 bets and over- you are betting that over the course of a longer session placing wagers on odd/even, Hi/Lo or Red/Black, that the distribution of results will be 50/50 (ie 10 black, 10 red in a 20 long session on red/black). That is to say that you expect any spikes or long runs of the same colour to be evened out by recurring events of the opposite colour in the long run.
This may not be the case, of course. Theoretically over the course of 20 spins you might see 20 reds which exposes the key flaw in this system: despite what D'Alembert thought (and what most people would experience on a day to day basis) a run of 20 reds is perfectly possible. The roulette wheel has no memory, whether it is a virtual roulette wheel or a wheel at Las Vegas, Monte Carlo or Macau. Each spin is a mutually exclusive event and there is a 50/50 chance on each spin that you will get either colour, (well slightly less than 50/50 as remember that there is an additional zero pocket in European Roulette -and 2 zero pockets in American roulette- which nudges your odds down to 18/37 and 18/38).
So bear this in mind. As with any system, we recommend playing them only as a method of building some rules into your play. Play methodically with a profit target and a stop loss limit that you have decided on BEFORE you hit the table, and this system is worth a test, just like any other. But understand it's flaws. Mathematically speaking, D'Alembert was of course incorrect in his overall assumption.
Now, enough of the theory. Let's look at how you would employ the D'Alembert System at the roulette table online.
So, say you place a £10 bet on High numbers (19-36) and you lose, add a unit on the following bet (so you bet £11 again on high numbers). If you win on the next bet, take your next punt down by a unit again, so you are back down to £10. Continue in this fashion until you have hit your profit target (or your stop loss limit!) or you get down to a bet of zero.
The overall idea is that you add a single unit when you lose a spin and take away a single unit when you win a spin. Don't double up your bets (this is the Martingale Betting System, a betting system which incedently increases the risk of your bets ramping up to a heart attack inducing level!)
Also known in roulette circles as a negative progression and insurance system. The idea, by whittling down your bets when you win, is to bank your profits on wins and wipe out losses with a higher wager if you are not so lucky.
Like any system, D´Alembert will not increase your odds when used. Sorry to be the bearer of bad news but we prefer to give you the facts rather than the myths. It is not a guaranteed way of making money and don't believe anyone who tells you that it will. Use with care, and employ it with your head and not your heart.
Would we use the system? Yes- but we would use it sensibly. First we would test it out on a free account at an online casino where you get a virtual balance. Risk: zero. Then, when we had got the hang of it, we would start testing it on a real money account but with strict profit and loss limit targets. Risk: contained.