PSIA is Pounds per Square Inch Absolute, as opposed to PSIG which is PSI Gauge. PSIA is absolute pressure. For example, normal atmospheric pressure is about 14.7 PSIA, so a PSIA device connected to atmosphere would read 14.7. PSIG is relative pressure, so if system pressure is 15.7 PSIA, and atmospheric pressure is 14.7 PSIA, then PSIG would be 1.0
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0 psia is used as a reference point for pressure measurements because it represents the absence of pressure, equivalent to a perfect vacuum. By using 0 psia as a reference, pressure measurements are taken relative to this baseline to accurately determine pressure differentials in various systems and processes.
0 mmHg is equivalent to 0 psia because both represent a pressure of zero relative to absolute vacuum. However, 760 mmHg is equal to 14.7 psia, not 0 psig. 760 mmHg is equivalent to atmospheric pressure, which is the reference point for psig.
To convert bar to psia (pounds per square inch absolute), you need to add the atmospheric pressure in psia to the pressure in bar. 1 bar is approximately equal to 14.5038 psia (standard atmospheric pressure at sea level).
PSIG refers to pound/force per square inch gauge, while PSI measures the pressure relative to a vacuum. If you want to convert a figure from PSIG to PSI, you would need to add 14.7psi to your PSIG figure, which will give you your PSIA result.
Distance from the Equator is measured using lines of latitude. The Equator is designated as 0 degrees latitude, and distances are measured in degrees, minutes, and seconds north or south of the Equator.
Latitude is measured in degrees North and South from the North to South poles. Longitude is measured in degrees East and West starting with 0 at Greenwich, England.