The most commonly reported methods of conducting penile plethysmography involve the measurement of the circumference of the penis with a mercury-in-rubber or electromechanical strain gauge, or the volume of the penis with an airtight cylinder and inflatable cuff at the base of the penis. Penile plethysmography ( PPG) or phallometry is measurement of bloodflow to the penis, typically used as a proxy for measurement of sexual arousal.