The Doppler is used for detecting blood flow acoustically and for making blood-pressure measurements indirectly using an inflatable cuff and sphygmomanometer. The method is like that used on humans; the Doppler functions as a stethoscope. Systolic pressure is measured by reading the pressure on a sphygmomanometer when the blood flow sound first returns as cuff pressure is lowered. Normally, only systolic pressure is measured. Diastolic pressure measurements can be made, but they are not very accurate and require lots of subjective judgment. Features: Built-in speaker Auxiliary headphone output Rechargeable battery Low-battery indicator 8.0 MHz to 9.9 MHz frequencies available Various welded-metal cases available