Biofeedback is a useful treatment for a variety of illnesses, although it is most commonly used to treat hypertension, tension headaches, migraine headaches, chronic pain, and urine incontinence. It can also be effective in treating obesity. Biofeedback uses instruments that measure physical or biological processes quantitatively and makes these measurements visible to the patient. This allows the patient to see progress toward achieving health goals and to correct undesirable behaviors before they result in serious damage to the body. Biofeedback methods include electroencephalogram (EEG), electromyography (EMG), heart rate variability (HRV), respiratory sinus arrhythmia (RSA), and skin temperature measurement. These are discussed in detail under their respective headings. Biofeedback has been shown to be effective in reducing symptoms of many disorders. It can also help patients learn how to control certain functions of the brain and body that they may not have known existed. For example, one patient reported that learning how to control his heartbeat with his mind had such a calming effect that he no longer needed to take medication after a heart attack! Biofeedback has been proven to be more effective when used in combination with other treatments.