text: The relation of equilibrium vapor pressure to the saturation vapor pressure can be thought of as a relative humidity measurement for the atmosphere.  As P/P increases, vapor will continue to condense inside a given capillary.  If P/P decreases, liquid will begin to evaporate into the atmosphere as vapor molecules.  The figure below demonstrates four different systems in which P/P is increasing from left to right.
  System A → P=0, no vapor is present in the system
  System B → P=P, capillary condensation occurs and liquid/vapor equilibrium is reached
  System C → P=P, P, as vapor pressure is increased condensation continues in order to satisfy the Kelvin equation
  System D → P=P, vapor pressure is increased to its maximum allowed value and the pore is filled completely
  This figure is used to demonstrate the concept that by increasing the vapor pressure in a given system, more condensation will occur.  In a porous medium, capillary condensation will always occur if P≠0.