Absolute pressure is zero-referenced against a perfect vacuum, so it is equal to gauge pressure plus atmospheric pressure.
Gauge pressure is zero-referenced against ambient air pressure, so it is equal to absolute pressure minus atmospheric pressure. Negative signs are usually omitted. To distinguish a negative pressure, the value may be appended with the word "vacuum" or the gauge may be labeled a "vacuum gauge."
So suppose you are in an ocean at height depth,your absolute pressure would be Pabs while your guage pressure would be simply abs, also you can say if at any point your total pressure is P your absolute pressure is P while your guage pressure is Pabs – Pamb.
