Earned Value (EV) is a function of the time and it represents the progress of a project. It's measured in units of economic value ($). Mathematically, the domain of the Earned Value (EV) is time and the range is economic value ($). The Earned Value (EV) is clearly associated with the Planned Value (PV) because the value that EV has, when a milestone is passed (or a goal is achieved), is the same that PV has in the same circunstances. In other words, when a unit of work has be done, EV adds the same value that was planned for that unit of work in curve PV, no matter how much was the cost of finishing that unit of work.