Measuring Ambient Pressure in MSG: How It's Done

Hello fellow enthusiasts,

Since I'm currently focusing intensely on problems related to charge pressure regulation (AFN), I was wondering today how the MSG (Manifold Absolute Pressure sensor) actually measures the ambient pressure.

Is there perhaps a second pressure sensor (in addition to the actual LD sensor) installed in the same black housing (in the MSG)?
It must also have a connection 'to the outside.' The control unit itself seems to be sealed.

Or is the ambient pressure simply 'measured' by the LD sensor in the meantime --from the moment the key is turned (ignition on) until the engine starts-- and then stored?
In principle, it would work because it is an absolute pressure sensor.

The question arises because I took various Log readings exactly one week ago (air pressure according to a precise barometer: 1010 mbar, reading in the VAGCOM log: 996 mbar --> within the measurement accuracy) and again today.
The air pressure today, according to the high-pressure system 'Bernhilde,' is 1050 mbar. However, the reading on the VAGCOM device still shows 996 mbar !

Where is the error here?

Best regards,
Kassen.

A separate sensor is installed.

The ambient pressure sensor is only used for altitude compensation and influences the load detection (LD) control system only via the target LD value. In other words, at high altitudes, the target LD value is reduced to prevent the engine from over-revving.