Absolute and Gage Pressure

Absolute and gauge pressure terminologies. The first thing is the difference between the two is the datum. The name "absolute pressure" indicates, this is relative to absolute zero pressure, right? We also call it vacuum, absolute zero, or vacuum, right? Gauge pressure is, it's relative to the atmospheric pressure. And I draw over here a graph. The y-axis is the pressure. This is zero pressure, vacuum. This is atmospheric pressure. So, let's pretend that I have a pressure over here that is represented by this line, right? So, the gauge pressure over here will be this P gauge, and this will be P absolute. Okay, so you can see from here that the absolute pressure cannot be negative, but the gauge pressure can be negative. And also, you can see from here that if you want to write an P absolute pressure, is equal to P atm plus P g.