Reliable reproducible values

The device provides with me reproducible values ​​which are in repeated measurements always within the specified measuring accuracy of 3 mmHg. I had no manifest error of measurement after about 20 measurements.
Unlike my previous unit of Rossmax the unit has a collar which, although has no metal brackets, but is partially rigid so that the cuff as good if not better can be attached to the arm.
Compared to my previous device, the device is much quieter, but also pumping more slowly on.

Diastolic value is compared to the old device more or less identical, the systolic value is always about 6 mmHg higher regardless of the order in which or on which arm I measure.
Which device closer to the actual value I can not judge - perhaps both units display the correct value, but since the Panasonic is slower, and thus a long time squeezes the arm, the systolic value (and only?) A bit higher - this I would like a plausible explanation.

I opted for the new device, because old regularly every 3-5 measurements produced my a faulty measurement - perhaps it pumps but on too quickly.