The cuff size must the appropriate for the blood pressure measurement to be accurate. The arm and the mercury or aneroid manometer must be at the same level as the heart. The patient should be seated for about 5 minutes with the back supported and with the arm supported at heart level. If the arm is not supported than readings are approximately 8 mmHg higher than those taken with arm supported. If the back is not supported, readings may be as much as 10 mmHg higher because of the isometric exertion needed to support the body and arm.
Inflate the bladder quickly to a pressure about 20 mmHg above the systolic pressure as recognized by disappearance of the radial pulse. Inflating the bladder too slowly may cause errors. Deflate at a rate of 2–4 mmHg per second; a slower rate of deflation may cause false high readings. If a second blood pressure reading is to be taken, the cuff must be completely emptied of air and the arm band removed and reapplied. Many erroneous readings are obtained if proper technique is not stringently applied.