Ekman, P., & Friesen, W. V. (1978). Facial action coding system. Investigator's guide: Paul Ekman ; Wallace V. Friesen. Consulting Psychologists Pr..

Ekman, Paul, and Wallace V. Friesen. Facial Action Coding System. Investigator's Guide: Paul Ekman ; Wallace V. Friesen. Palo Alto, Calif.: Consulting Psychologists Pr., 1978.

Ekman, Paul, and Wallace V. Friesen. Facial Action Coding System. Investigator's Guide: Paul Ekman ; Wallace V. Friesen. Consulting Psychologists Pr., 1978.