LooTe, as far as my understanding of the equal percentage valve it is the equal percentage increment of flow for a equal lift.

From http://www.boacalgary.com/artvalve.html

Equal Percentage Characteristic - In a valve having an equal percentage characteristic, like movements of the valve stem at any point of the flow range changes the existing flow an equal percentage regardless of the existing flow.

Example:

Suppose a valve stem has been lifted 30 percent of its total lift and the flow at this time is 3.9 gal/min. Now assume that the valve opens an additional 10 percent of its full travel and that the flow increases to 6.2 gal/ nun or a 60 percent increase. Next, suppose that the valve stem moves an additional 10 percent so that it is now 50 percent open. The flow now will be 10 gal/min or another 60 percent increase in flow.