Technical analysis focuses on trend analysis and explains how basic trend-following techniques are used. 

Flip through the individual charts: 

Prices retrace part of the preceding trend before continuing in the original direction. These counter movements tend to fall within certain predictable parameters. The 50% retracement is one of the most common. 

The formula for defining a 50% retracement is:

Highest price on a chart – lowest price on a chart × 0.5 = possible 50% retracement