The indicator consists of two lines – %K and %D. %K is the fast primary line, usually with a period of 14. It is additionally smoothed out using the “slowdown” parameter with a period of 3. This smoothing improves the accuracy of the indicator’s signals.
%D is a slow line. It is calculated as the moving average from the %K line and has a period of 3.
These lines can move between 0 and 100. In doing so, they cross 20 and 80. The zone below 20 is the oversold zone and above 80 is the overbought zone.