What is the {CHARGE PRESSURE} indicator?

I would like to purchase a boost pressure gauge.
Do you have any recommendations for what is particularly recommended?
Can I install it myself? Are there instructions?

Thank you in advance.

Hi

. . . the measurement range is more important.
To prevent the pointer from immediately leaving the scale (or sticking at the end, making it difficult to determine the exact amount of overpressure), I would recommend choosing a pressure range with approximately 30-50% reserve.

For 90, 110, and 115 horsepower, 1.5 bar is sufficient.
The 130 and 150 models have significantly higher boost pressures, so I would prefer a 2-bar gauge.

Even though a suction area on the display for the diesel engine initially seems nonsensical:
In the idling mode, you can use this to determine if the air intake is no longer clear (e.g., due to leaves, filters, etc.), and with the newer models with "parking anti-vibration flap" (ALH, AHF, ASV . . . ?).
can it be monitored in real-time, including its full opening and functionality, when it is stopped?

[Translating...]Ganz nebenbei kann man mit dem negativen Bereich die Unterdruckpumpe prüfen wenn man das Instrument an derselbigen anschließt (z.B. an einem freien Platz am Ventil nach der Pumpe.) Ist ganz interessant z.B. beim Bremsen den Druckverlust/Aufbau etc. zu beobachten.