Technical Indicators - Fibonacci Retracement

Arguably the most heavily used Fibonacci tool is the Fibonacci Retracement. To calculate the Fibonacci Retracement levels, a significant low to a significant high should be found. From there, prices should retrace the initial difference (low to high or high to low) by a ratio of the Fibonacci sequence, generally the 23.6%, 38.2%, 50%, 61.8%, or the 76.4% retracement.

For the examples of this section, the S&P 500 Depository Receipts (SPY) will be used based on the logic that the S&P 500 is a broad measure of human nature, thus the Fibonacci sequence should apply very well. Nevertheless, the Fibonacci sequence is applied to individual stocks, commodities, and forex currency pairs quite regularly. The chart above shows the 38.2% retracement acting as support for prices.
Note that a trendline was drawn from a significant low (beginning of trend) to a significant high (end of trend); the trading software calculated the retracement levels.
The chart below of the SPY's shows that Fibonacci Retracements can be used to retrace downtrend moves as well:

Notice after the bottom in the S&P 500, that price rallied to the 23.6% retracement level and then was promptly rejected downwards. After breaking resistance a few months later, the 23.6% retracement became support. Price rallied up to the 50% retracement level, where it ran up against resistance. Price continued to fluctuate between the 38.2% retracement level (acting as support) and the 50% retracement level (acting as resistance).