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If someone is at sea level and they put ten pounds of air pressure into a container does the container now have 10 + 14.5 = 24.5 pounds of air pressure. Do we not add the atmospheric pressure? Seems like the container had 14.5 in before the ten was added. I have a feeling there is a simple something I am over looking here. How much air pressure is in the container.

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  • $\begingroup$ Are you familiar with the difference between gauge pressure and absolute pressure? $\endgroup$ – tpg2114 Oct 16 '17 at 0:12
  • $\begingroup$ No I am not. Apparently, the answer is in semantics then. I thought it would be a simple answer. So now I know. $\endgroup$ – Lambda Oct 16 '17 at 0:19
  • $\begingroup$ If you have a totally flat car tire, and the auto mechanic asks you what the current air pressure in the tire is, do you tell him that it is 14.7 psi? $\endgroup$ – Samuel Weir Oct 16 '17 at 0:29
  • $\begingroup$ My conversation with the mechanic would be different than one with a physicist. Hopefully, the physicist would think a little deeper. $\endgroup$ – Lambda Oct 16 '17 at 0:39
  • $\begingroup$ Related: Gauge pressure vs. absolute pressure? $\endgroup$ – Alfred Centauri Oct 16 '17 at 1:09
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there are two different conventions that people use to express pressure. "absolute pressure" includes the contribution of atmospheric pressure and "gauge (also spelled "gage") pressure" does not. So a sensor that is calibrated to read gauge pressure will indicate zero on the readout when it is sitting in ambient air at 14.7 PSI, and its readout will specify PSIG, meaning pounds per square inch GAUGE. A sensor that is calibrated to read absolute pressure will read 14.7 PSI when it is sitting in ambient air and its readout will specify PSIA, meaning pounds per square inch ABSOLUTE.

This means that (PSIG) = (PSIA-14.7)

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