I know its weird but there are BOOKS on this stuff.
I recommend "Maximum Boost" by Corky Bell for beginners and intermediates.
Also, Looks like that thing reads bar and temps in C.
I'm guessing its using the MAP (manifold absolute pressure) sensor signal on the chargepipe and not the MAP on the intake manifold, because your bar for idle vacuum is higher than what it would be in the manifold. ( -.33bar or so depending on your altitude...)
OR it could be reading requested boost figures from the ECU. Which would be useless especially if you have a piggyback system (JB4 or something)
A Mechanical Boost Gauge is the only way you can read what's in there...Digital gauges can always be manipulated or shown incorrect values. BUT on a newer Bimmer its hard because there is no vacuum port to use on the intake manifold
