The instruments (OP, OT, VAC) in these aircraft are "off the shelf" components that are purchased directly from suppliers and fitted to the aircraft. It's unlikely that Cessna or the POH will go into detail on how they are constructed, just as your car operator's manual will not tell you how the speedometer is constructed.
Perhaps you would get the information you need from an aero maintenance company - particularly one which services your flying school's aircraft. Most engineers are happy to educate pilots on these kinds of issues.
Good luck,
O8