Some of the popular breadth indicators are:
- Advancing - Declining Issues
- Advance/Decline Line
- Advance/Decline Ratio
- Breadth Thrust
- McClellan Oscillator
- The McClellan Summation Index
- New Highs-Lows Cumulative
- New Higs-Lows Ratio
- New High/Lows
Once you understand breadth indicators, one can develop a market timing model based on such indicators. Such market timing models indicate zones where turns can appear in market and can identify safer periods for using long or short strategies. I developed Market Monitor after studying the breadth indicators commonly used. Market Monitor is a breadth indicator. The key difference between Market monitor and other breadth indicator is that MM uses significant moves to look at breadth.
The Novice Bear has adopted the Market Monitor concept in Blocks and put together a video on how to use it on his site. It is a good video explaining the basic idea.