The microprocessor controlled Quattro™ II provides interferential (4-pole), premodulated (2-pole interferential), medium frequency (Russian), EMS and TENS waveform. You can choose between several different amplitude modulation options. The interferential and premodulated modes offer frequency modulation as well as a static frequency option. (2-year warranty) Caution: This is a Class II Medical device and Federal law Restricts this device to sale by or on the order of a licensed health care professional.