The two complex poles with the root locus that cross the imaginary axis are the poles that are of interest to us. These two poles are referred to as the short period poles. Click on either of these two lines and drag the point along the line to determine the following: The damping when the gain is zero. This is the open loop damping. The gain when the damping is zero (when the line crosses the imaginary axis). The gain when the damping is 0.35. A damping of 0.35 is often the minimum required damping for the short period poles