Pressing B or pointing at the altimeter know and clicking causes the
altimeter to change the altimeter baro setting (kollsman window) to a
value so the altimeter will read the runway altitude. If you want to
adjust the altimeter setting you have to go to the menu Aircraft -
Realism & Reliability - Realism and set the value there. If you want to
change the atmospheric pressure go to World - Advanced Weather -
Pressure and change the pressure. If you do this on the ground, you'll
note that the altimeter reading no longer reads the airport altitude.
If you hit the B key or use the mouse pointer to click on the altimeter
knob, the altitude reading will reset to the runway altitude and the
kollsman window will have changed correspondingly.
Regards,
Bob...