There are several reasons for this:

   Blood pressure measurement is not fixed.

    Blood pressure changes at every moment of the day and even from one minute to the next.

  It is impossible to compare two blood pressure meters.

To obtain a reliable measurement, it is important to take 3 successive measurements (1-2 minutes apart) and to average them to obtain the most realistic blood pressure possible.

You can use the free mobile applications "suiviHTA" and "DepistHTA" to help you take your blood pressure and follow its evolution.