I know that the average PSI at sea level is 14.7 PSI, I just don’t understand why gauges and other PSI measuring equipment dont account for outside atmospheric conditions.
For example, if you were filling a scuba tank at sea level, the gauge would say 0 PSI instead of 14.7. And when you do fill the tank up by 100 PSI (I don’t know how much a scuba tank holds), it would say 100, not 114.7.
It’s the same with vacuum chamber gauges. Instead of going from 14.7-0, they go from 0 to around -30 PSI. Where is the extra 15.3 PSI coming from? I assume that it is just standard to start at 0 PSI for all gauges, but it’s a bit confusing. Because if you were were on top of a mountain then the gauge wouldn’t be accurate.
In: Physics
They do account for it in more technical fields you will often see 0psi(a) or 0psi(g). (a) means absolute in which case you would be discussing the pressure compared to atmospheric. (g) refers to gauge, as in this is the pressure of the system discounting the pressure of air, as the gauge has already been calibrated to account for it.
This is done because it is easier to keep track of, and it just makes more logical sense. For instance if I held my finger an inch from your skin and asked do you feel pressure you wouldn’t answer “Yes the 14.7psi from the air”.
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