Stock screeners allow traders to screen the entire market for stocks that conform to certain criteria to meet the needs of the trader. They are indispensable for modern stock traders, and can be either web-based or stand-alone tools. One of the benefits of web-based screeners is that upgrades tend to be automatically available.

If you consider how stock screening was carried out some years ago before the advent of the modern online stock screener, you will begin to understand the benefits that these systems have provided in enabling trading opportunities to be identified in seconds. Think of pouring over the stock exchange sections of newspapers, of trying to make sense of radio, real-time stock quote machines and of charting graphs by hand.

These manual procedures allowed very few stocks to be examined in a given timeframe, and you would be lucky to spot any stock to meet your criteria, let alone compile a useful Watch List. By allowing today's traders to set criteria and automatically screen out all companies that do meet these criteria, today's stock screeners can examine tens of thousands of stocks in a very short time. Results are virtually instant.

The filtering criteria used can detect stocks suitable for growth, for short or long-term earnings, or whose values will increase in a relatively short period of time. Using technical criteria to spot key reversals and breakouts can boost your stock earnings several-fold. If a trader feels a specific criterion to be important, then the stock screener will find a list of stocks that fit, and if several criteria are used in the same search, stocks with very specific properties can be identified.

There are two specific types of screening that can be carried out: by use of either fundamental or of technical criteria, and each can be made available either as end of day or real time intraday screening. Most normal stock screeners utilize fundamental criteria, although elements of technical analysis can also be included to fine tune the screening.

So how should these screeners be used? Let's have a look at the technical criteria that can be used in filtering the stocks that you want on your Watch List. You could start by trying to find trending stocks, or those that will break out above or through resistance levels. The criteria to use in your filtration in order to screen for these could include:

• Stock trending up
• Rising on unusual volume
• Price crossed above resistance line
• Price has touched support line (It is likely to climb again)
• Price has reached new highs

Many of the fundamental screeners can be obtained free although if you want a real-time technical screener then you will likely have to pay a nominal fee. However, although it is normal for stock screeners to be predominantly one or the other, there are screeners available that can be used with both fundamental and technical criteria. This expands the type of screening available to you, and you should never buy a stock unless both the fundamental and technical criteria are both positive for the stock. You will achieve better results if you screen the stocks for both types of criteria, and for that you will need either a combined stock screener, or one of each type.

Stock screeners are essential for screening in today's markets because most professionals actually underperform the market due to human influences. A machine-based model can filter out human weakness, such as believing press forecasts, and produce better results assuming that the criteria, or variables uses, are those that affect the direction of stock prices in the future.

Given that is so, stock screeners are a must for the modern investment professional and novice alike.