a downhole well valve having a variable area orifice is flow area adjusted by a sliding sleeve that is axially shifted along a tubular housing interior in a finite number of increments . a hydraulic actuator displaces a predetermined volume of hydraulic fluid with each actuator stroke . an actuator displaced volume of fluid shifts the flow control sleeve by one increment of flow area differential . an indexing mechanism associated with the sleeve provides a pressure value respective to each increment in the increment series .