Glossary: Relative Pressure

P/P₀, where P is the absolute pressure and P₀ is the saturation vapor pressure of the adsorptive at the experimental temperature. This is commonly used, for example, as the x axis on isotherm plots of N₂ uptake at 77 K. At this temperature, P₀ for nitrogen is 1 bar (or 0.1 MPa) and so the relative pressure is 0 – 1 in the pressure range 0 – 1 bar.