Roulette: Betting strategies and tactics: Using the dozen bet

There are two versions to this system, single dozen bets and double dozen bets. In the single dozen bet version, the player uses a progressively incrementing stake list starting from the casino table minimum, to the table maximum. The aim here is to use a single dozen bet to win before the stake list ends. Many techniques are employed such as: betting on the same dozen to appear after two consecutive appearances, betting on the dozen that has appeared most in the last 15, 9, or 5 spins, betting on the dozen that, after a long absence of 7 or more spins, appears for the first time. The double dozen bet version uses two dozen bets and half the stake list size of the single dozen bet version.

From Wikipedia's

Contents - Roulette