Hi again rudderrudderrat and thnx again for your reply!
Slowly i'm getting it..The atmosphere does NOT behave in a fixed volume way but this one varies according to the temperature so to keep a constant pressure.
As you said the Altimeter mesaures PRESSURE altitude. That's why we set the QNH every time we fly in order to know our true altitude (without counting now temperature variations of more than 10°).
So correct me if i'm wrong. But may be i got it now:
The changeover between EAS and MACH will always come at the same
PRESSURE altitude, which indeed we can find at
different REAL altitudes which depend on density, temperature ecc ecc.
Did i get it?
Sorry if i keep on asking but i'm starving to get to the solution!
Thank you guys again!
bio161