FraPre wrote on Dec 25^th, 2018 at 3:52pm:

Problem clarified, the two Altimeter are not synchronized so I just focused on one side and the Stby Altimeter.

A small tipp here, there is a keyboard command in P3Dv4 to set all altimeters to standard.
I just set my main altimeter manually and then set the rest using that key command, that saves me the hassle of rotating the altimeters for a looooong time at high/low pressure.  ;D