Feature in a breathing tracing that changes during arousal. It is a linear measure of the breathing waveform over a specified period time. RLLs are inversely related to autonomic nervous system activation. This is because the typical breathing response to stimulation or orientation is a suppression in the rate and amplitude of breathing. It was first reported in the PDD literature by Dr. Howard Timm, and several studies have since supported the use of this measure in deception tests. The use of RLL as a deception criterion presupposes stable respiratory patterns. See: Timm (1982).