It's a 3phase 240v delta service, with the center of one phase taken as neutral for 120 volt loads. The 208 v measured to neutral is(was) called the "stinger leg."
Automobile voltmeters draw more current than multimeters. Measure the current into your meter when it is connected across a reasonably stiff 12-volt source. That is the current for full-scale deflection, and what you must come up with by reducing the value of that 68-something resistor and...
There were/are the applications ABEL and PALASM for PAL development. They show up as freeware now and then.
I remember feeling like the king of nerds when several pages of logic equations and wishful-thinking were burned into a breadboard of those things.
That barometer seems to use an SPI connection.
IF your flight recorder can accept SPI inputs and IF you have access to the recorder's code, you can do it.
Connection by UART seems unlikely, but I don't know your level of expertise.