The partial vacuum can be measured in Pascal or Torr, or as a percentage of [atmospheric pressure]? using the bar or barometer? scale.
Degrees of vacuum:
[Atmospheric pressure]? = 760 torr
[vacuum cleaner]? = around 300 torr
mechanical vacuum pump = around 10 millitorr
near earth outer space = around 1 x 10-6 torr
pressure on the moon = around 1 x 10-8 torr
interstellar? space = around 1 x 10-10 torr
Creating a vacuum:
When creating a vacuum, the matter in the volume being evacuated flows differenly at different pressures based on the laws of fluid mechanics. Initally a compression pump can be used to remove the material, as the molecules are interacting with each other and will push on their neighboring molecules. when the distance between the molecules increases, the molecules interact with the walls of the chamber more often than the other molecules, and compression pumping is no longer effective.
At this stage, we have entered a state called molecular flow, where the directionality of each mloecule is basicly random. Three basic ways to remove the remaining gas are by converting the molocules of gas to their solid phase (by freezing them, called cryopumping? or cryotraping?), converting them to solids by electricly combining them with other materials ([ion pumping]?) or using a specialized machine called a turbopump?.