Depending on the polygraph manufacturer, this mode may also be labeled as Auto, Auto-Center or Auto EDA. It is a setting for the electrodermal activity channel, which uses a combination of filtering that may include; a low-pass filter, a high-pass filter and/or a smoothing filter. It is intended to keep the electrodermal tracing near the center of the display by filtering out low frequency changes that are typically a consequence of shifts in tonic skin conductivity. All modern polygraphs have this feature. While the self-centering action of the automatic mode is attractive to many PDD examiners for practical reasons, it has been criticized for altering data in ways that affect data analysis. Most modern instrument manufactures include both a manual and automatic mode.
