If two cuff sizes fit, use the larger one.
The brachial artery is the major blood vessel of the (upper) arm. It is vital to find the correct location of the brachial artery when taking a blood pressure. To find the brachial artery, turn the palm face up and follow the line of the pinky upwards just past the crook of the elbow.
Watch this video on how to find the brachial artery.
Allow room for no more than two fingers underneath.
Make sure you have not consumed food, alcohol, caffeine or exercised or smoked for at least 30 minutes before taking the measurement.
Keep feet on the floor. Do not cross your feet.