Definition of a Function. A function is a relation for which each value from the set the first components of the ordered pairs is associated with exactly one value from the set of second components of the ordered pair. Okay, that is a mouth full.
Master cylinder without booster. Single bore master cylinders: These unboosted hydraulic Master Cylinders are actuated by foot effort, via the brake pedal. The brake pressure is related to actuation force and depends on the piston bore size: the smaller the bore, the higher the pressure.
1 Master cylinder mounted: Another type of proportioning valve is the master cylinder mounted. It is screwed on the fluid ports that are located between your car's brake lines and master cylinder.  Combination valve mounted: The last proportioning valve type is the combination valve.