The D'Alenbert System

This is a negative progression, meaning that you increase your bets as you lose, rather than as you win, and it's an insurance system, meaning that you decrease the amount of your bets as you win.

Again, simply stated - increase as you lose, decrease as you win.

You must know in advance what you consider a "unit" of betting to be. For example, you could decide a unit is the minimum bet allowable, or you could decide it's the minimum bet plus a certain amount. The number you choose to be your "unit" should vary depending on the game you're playing and its odds.

Either way, in the D'Alenbert System, a blending of the Martingale System and an Insurance System:

You raise your bets by one unit each time you lose and
You lower your bets by one unit each time you win

You must have a sizable bankroll in order to play a negative progression system effectively. By increasing your bets as you lose, you are hoping to recover from a losing streak with one powerful win. This is a high-stress method of gambling that occasionally yields worthwhile rewards.

By combining the insurance system, typically considered a "play it safe" method, you're attempting to balance the risk and counter your previous or projected losses by pulling a little profit off the table each time you're able.