Slow (Preferred) Stochastics are derived from Fast Stochastics. If we take the %D computed above and rename it to %K, and then smooth this line by using a three period modified Moving Average, we have the new slow, Slow Stochastic line, %D. These two lines make up the indicator called the Slow Stochastic, created by a modified Moving Average smoothing. This is what I use ("Preferred").