Do you know blood pressure is very dynamic. A reading can change 10 or even 20 points over the course of seconds. Thats why the current blood pressure guidelines recommend waiting one minute, retaking the reading, and averaging the two numbers. If the systolic values (the first number in a blood pressure reading) are more than around 10 points apart, consider doing a third reading a minute later. Averaging three values will likely provide an even more trustworthy result.

AHAs list of blood pressure measuring mistakes. Any of these errors may elevate your reading by several points (even as much as 10 points, in some cases), although they are generally not additive.

1. Having a full bladder. An uncomfortably full bladder might increase your reading.
2. Having no support for your back or feet. Slouching or dangling your feet when sitting can increase your reading. Make sure you sit in a chair with your back supported and feet flat on the floor or a footstool. At home, dont sit on a sofa or reclining chair.
3. Sitting with crossed legs. Crossing your legs squeezes the large veins in your legs, which may raise the reading slightly.
4. Not supporting your arm. Your arm should be totally relaxed so your biceps (upper arm) muscle isnt contracted. Be sure to position your arm on a chair or counter, so that the blood pressure cuff is level with your heart. Also, dont clench your fist.
5. Wrapping the cuff over clothing. Depending on the thickness of the fabric, putting a cuff over clothing can boost the reading by quite a bit. Wear a short-sleeved shirt (along with easily removable layers, if youre chilly in the doctors office) so the cuff is placed on your bare arm.
6. Using a cuff thats not the correct size. Many people need a large-sized cuff. Using one thats too small will be uncomfortable and may elevate your pressure by several points. Note that models with upper-arm cuffs are more reliable than those that fit on the wrist.
7. Engaging in conversation. Chatting during the measurement — or even actively listening — can boost blood pressure.