B757/767 cabin alt
On the overhead panel of the B757 and B767 there is a group of 3 round dials in the pressurisation panel.
The left one is cabin diff pressure
The middle one is cabin altitude
The right one is cabin rate of climb/descent.
Does anyone know if these are self contained? Are they worked from an internal input of cabin pressure?
OK the differential pressure might need an input from the ADC system, but surely the cabin alt would use a very simple barometric altimeter sensing cabin pressure in situ?
I am guessing it would read altitude based on 1013/2992 standard pressure?