My neighbor suggested I try their TENS device when I suffered a severe case of sciatica. I loved it and since I often play and work hard and can get pretty sore, decided to buy my own. The instructions are quite specific as to where to place the plus (+) pad and where to place the negative (-) pad. But I give this device a four because the company "cheaped" it in an important area - the two probes you plug into the pads are no longer color coded. They are both white and have very. Very small + and - symbols molded into the plug. VERY small. One might say TINY. I would suggest to my friends to buy a TENS unit but not from this manufacturer.