World and people

What you are really looking at is not the difference between analog and digital implementations of the same thing, but rather the difference between devices based on entirely different operating principles. It is not just a matter of the accuracy of the pressure sensor, because unlike in a tire gauge, the pressure sensor in a cuff-type blood-pressure monitor doesn\'t sense your blood pressure at all. Rather, it reads the air pressure in the cuff, from which the instrument indirectly infers your blood pressure, often with an error much greater than that of the pressure sensor itself.

The different types of instruments use completely different inference mechanisms, which is why they sometimes get different readings, even if the pressure sensors themselves are accurately calibrated. This has nothing to do with analog versus digital, because over the long history of manual and automatic blood-pressure-monitoring devices, analog and digital methods have been applied to both commonly used inference mechanisms.

http://www.profigroup.com/Electronics/Small-home-appliances/blood-pressure-device.htm