Human blood pressure is not a constant parameter. For completely normal physiological reasons, blood pressure can vary by up to 30 mmHg over a short period. It is therefore possible for the pressure to fluctuate between two measurements. In fact, it is very difficult to take consecutive measurements under the same conditions. This type of test usually gives different results due to the instability of physiological conditions and secondary factors (discussion, noise, movements, etc.).
This is why the average of several results measured on several days under comparable conditions at the same time is considered to be the real blood pressure. If, for example, you test blood pressure one hour after the evening meal over three consecutive days, you will not find significant differences. The average of these results more accurately reflects your blood pressure.
To limit these variations as much as possible, be sure to follow the precautions for use.
*credit to Sylvain of iHealth Labs EU