Some blood pressure monitors that measure blood pressure on the wrist, it can provide decent accuracy. If you use them properly, it will not be a serious error. But in the official guide cardiologists when measuring blood pressure in the arm cuff is not recommended to use a wrist or finger.
Tonometer wrist is very sensitive to changes in body position. When blood pressure measurement arm and the wrist should be strictly on the level of the heart. And even if you do everything correctly, your blood pressure is likely to be overstated and is calculated with a certain error. This is due to the fact that the artery in the wrist much narrower and located more superficial than the upper arm.
Some people have a lot of weight, and the amount of hands so big that the shoulder is difficult to measure blood pressure. We need a very wide cuff.
Someone measurement on the shoulder seems to be too painful. But in such cases it is necessary to use a blood pressure cuff for the wrist.
Normally blood pressure measured at home is different from what obtains doctor on internal reception. It would be helpful to bring your blood pressure cuff for the wrist to the doctor, that he compared the readings. Tonometer itself during the time necessary to check the service center.