LifeSource Arm Blood Pressure Replacement Cuffs are for use with the AnD Upper Arm Blood Pressure Monitor with Bluetooth Technology. They are available in four sizes: small, medium, large and extra large. Using the correct size cuff is important for an accurate reading. A cuff that is too large will produce a reading that is lower than the correct blood pressure; a cuff that is too small yields a measurement that is higher. With your arm hanging at the side of your body, measure the circumference of your upper arm at the midpoint between the shoulder and elbow