As per the given formulas of schedule variance and cost variance. The schedule variance if is positive then you are ahead of schedule and vice versa. For the cost variance positive the project is under budget and for negative it is over budget. This formulas depend upon the the budget if they are equally distributed at every phase of the project. But there is a possibility that the initial phase for eg. Buying materials costs more at the start of project but cost low in the manufacturing of the device. So according to that the initial phase if we spent more and work done is left as the manufacturing is still to be coverd. This means that you can be over budget at the initial phase but it is possible that you can be on budget when the project is to be completed or complete. So how do you decide by the measurement of the EV, SV and CV that you are calculating at any point of project is same in reality after the project is completed?
It is important to note that Earned Value (EV) is dependent on the percent completion of the project and not necessarily the specific date that the cost is being evaluated. That is, when looking at Cost Variance (SV), if you are spending heavily early on, it can be that 25 percent of the project is completed in the first week while the rest of the project is completed over the span of 10 weeks. Therefore, the EV would be greater in that first week as a percentage of the original budget and can still be accurately measured against the actual costs. As spending goes down, the percent of the project's completion is not increase as rapidly, meeting the slower spending observed in the actual costs.
Any skewed costs over time hold no bearing when considering the Scheduled Variance (SV). SV, similar to EV, both consider only the percent of the project completed. SV is dependent on the EV and Planned Valued (PV), which are evaluated by the actual and predicted percentage of completion, respectively. In this sense, if more is spent early in the project than predicted, and you believe that increased costs doesn't increase the progress of the project, the costs wouldn't affect EV. It will evaluate out to however far the project progressed and compare it to how far it was expected to progressed by that specific date.
Earned Value Management (EVM) is a technique that can be used to measure project performance against the project baseline. This technique can be considered by insight to be one of the best practices areas for monitoring project performance from both a cost and schedule perspective. It is always important to think about two things, ahead of schedule vs behind schedule and over budget vs under budget. With PV, AC, and EV, some calculations can be done like the Schedule Performance Index (SPI), and Cost Performance Index (CPI). For both SPI and CPI > 1 is good and if it <1 is bad. For example, if we are in a hurry, for both cost and schedule and we subtract instead of dividing so we can get the variance. These calculations can help a project manager identify problems early and be more proactive and reactive.
EV, SV, and CV are mainly used as estimates so that the PM and stake holders can know where the project is at, and how it is doing. These values allow the PM to adjust, and make changes so that the project can be successful. As Jdc stated previously, Earned Value is dependent upon the percentage of work completed multiplied by the original budget of the project. Therefore to answer your question the values you calculate are simply a guideline to know where you at in the completion of your project. You cannot actually compare these values to what you will net gain upon completion of the project, but by looking at the SV, EV and CV you will be able to know if you need work harder and how much you can spend.
Earned Value Management highly depends on quantitative project planning. This is not practical for some novel and agile projects. Some modern projects which are always open to change utilize methods such as scrum or agileEVM. EVM also has other limitations and is not much used outside government/regulatory project settings anymore. EVM is complex, provides a misinterpretation of value, and does not include the importance of quality.
