The BF4B Doppler Blood Flow Detector is optimized to detect blood flow in the arterial and deep venous systems of the extremities. Applicable in the clinical assessment of deep venous thrombosis and valvular incompetency. Useful to locate vessels, take weak pulse, and assess vessel patency. The ultrasonic frequency is approximately 5.3MHz. Powered by a 9 volt alkaline battery, Model BF4B weighs 6 ounces and is 4.7" x 2.5" x 0.9". Contains two outputs to drive one or two headset stethoscopes, an external speaker, or a tape recorder. Battery, headset, and carrying case included.