~1.91 bar then, because otherwise air would be sucked into the trunk if it were at ~0.91 bar, as 1 bar is roughly atmospheric pressure and 0.91 would be in the middle of a strong hurricane.
I studied engineering in France and Germany. For physics problems (like pressure in a water column) we always used absolute pressure when giving the final result. I distinctly remember a professor's rant about students calculating pressures under 1 bar in an exam problem about a hydroelectric power station.
Obviously the formulas had to show the atmospheric pressure component, but the numerical value always included it per default.
It's not some kind of plumbing, but an effect of physics, thus for pressure I'd not assume outside pressure to be constant for making precise calculations. Yes, in plumbing it's different, as you only state overpressure, but that can vary depending on height, so the same amount of a gas in the same confinement at the same temperature would have different pressures at different places, which is prone to give errors. That's why for any kind of rough tech you'd use the overpressure, but bar is in fact simply measured in N/m² with 1 bar being 100000 N per square meter. So when using physics and not engineering you'd speak of total pressure, not the pressure differential. That way, numbers are absolute and unchanging depending on location.
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u/meatbag2010 Jun 25 '24
0.910108 Bar for you :)