This is a piece of history right here, a fully mechanical vibrato with a built in volume pedal. You can use it as a stand alone volume pedal without the vibrato turned on. The vibrato is a fixed intensity with a variable speed dial on the side. As you increase the speed you hear the motor pick up speed as well. A truly unique sounding vibrato with a ton of character. At this point in it's age at full speed the vibrato is inaudible, signal still passes but you cannot hear the effect. This is an old mercury can trem, so that has long since dried up, and been substituted with windex by a repair tech. This is a widely known substitute for mercury. This is definitely a must have pedal for anyone who loves pedals.