The unit of measurement is called millimeters of mercury which is a measurement of pressure also used in blood pressure.
Compression in flooring means.
Compression ridging is typically due to a substantial increase in wood moisture giving rise to over expansion within a wood floor e g a condition wherein expansion of wood exceeds the free space available between flooring boards.
The first definition you need to know is noise floor.
Compression levels are indicated with a range of numbers like 20 30 mmhg which means that the amount of compression will not fall below 20 mmhg and not exceed 30 mmhg.
When it comes to floors strength often relates to compressive strength the capacity of a flooring material to withstand heavy loads and resist compression density materials being pressed together.
The noise floor is the amount of ambient noise in the environment and the residual electronic noise present in the sound system.
Compressive strength looks at how much of a load a floor can handle and is usually reported in relationship to a specific technical standard.
Ambient noise includes wind traffic people talking people moving around any natural noise in the environment.
These will explain why compression needs to be used.
They are also commonly made from plastic and stainless steel.