Following from overshoot and undershoot is clipping. This explains the persistence of the overshoot and undershoot. The pilot community uses acronym UNOS (undershoot North overshoot South) to memorize this rule. The undershoot trajectory is defined by the steepest allowable trajectory. The undershoot trajectory also has the highest peak heat flux and dynamic pressure. Consequently, the undershoot trajectory is the basis for selecting the TPS material. Repolarization of the membrane potential continues, resulting in an undershoot phase or absolute refractory period. This is also commonly referred to as an action potential's undershoot phase. When they are lower than the final value, the phenomenon is called ""undershoot"". The undershoot strategy is to take smaller sticks and build up to the target stick.