psi, psig, psia

not letters of the greek alphabet
not odd names people pick for their kids

they are pressure abbreviations. pressure seems to be something that needs a lot of units for whatever reason. SI unit: pascal (Pa)... oither units: bar, pounds per square inch (psi), barye (ba), atmosphere (atm), millimeters of mercury (mmHg), inches of mercury (inHg), millimeters of water, centimeters of the water or mercury, torr... almost endless it seems.

well just in case you ever end up seeing some odd deviant of psi check out wikipedia on psi. apparently psig is just what the guage reads. you can get more specific and say if the guage is reading relative to a sealed chamber at 1 atm (then it would be psisg, for sealed guage) or relative to the pressure around the gauge (then it would be psivg, for vented guage). the psig doesn't specify vented or sealed. oh ya and psia is guage pressure plus local atmospheric pressure.