[taseal]

Originally Posted by tgrayson

The Instrument Flying Handbook , under Pitot-Static Instruments, Sensitive Altimeter says

Notice is says "absolute pressure"? That means relative to zero pressure, which would be vacuum, again suggesting an evacuated chamber. Anyway, it later says: (taseal: this part I don't understand how its relative to 0 pressure?)

Principle of Operation
The sensitive element in a sensitive altimeter is a stack of evacuated, corrugated bronze aneroid capsules like those shown in figure 3-3. The air pressure acting on these aneroids tries to compress them against their natural springiness, which tries to expand them. The result is that their thickness changes as the air pressure changes. Stacking several aneroids increases the dimension change as the pressure varies over the usable range of the instrument.

that was the best one. going to get my inst book to find it. that was all I neeed