A variable geometry turbine controller for operation with a variable geometry turbine including a variable geometry member located in an inlet of the turbine, an actuator operative through a range of actuation positions to move the variable geometry member through a range of variable geometry member positions that extends between a hard-stop closed position and a hard-stop open position, and that includes a reference position corresponding to desired flow conditions, and a sensor device configured for sensing actuation information indicating the actuation position of the actuator, comprising: a memory device operative for reading and writing information; and a processing device operative with the memory device to write and read positional information, including reference-position information identifying sensed actuation information corresponding to the reference position, and including variation information identifying a baseline to determine variations in the accuracy of the reference-position information; wherein: the variation information includes measured displacement-range information regarding a displacement range over which the actuator operates to force the variable geometry member between the hard-stop closed position and the hard-stop open position; the reference position is the lowest flow position to which the processing device will direct the actuator to actuate the variable geometry member during normal operation of the turbine the processing device is operative to intermittently direct the actuator to actuate the variable geometry member to the hard-stop closed position, to read the actuation information sensed by the sensor device with the variable geometry member at the hard-stop closed position, and to re-establish the reference-position information by reading the sensor information while the variable geometry member is at the hard-stop closed position, and calculating what the sensor information should be with the variable geometry member at a predetermined angular increment from the hard-stop closed position; and □ the processing device is configured to re-establish the reference position only when newly measured displacement-range information varies from previously measured displacement-range information by at least a predetermined standard. a memory device operative for reading and writing information; and a processing device operative with the memory device to write and read positional information, including reference-position information identifying sensed actuation information corresponding to the reference position, and including variation information identifying a baseline to determine variations in the accuracy of the reference-position information; wherein: the variation information includes measured displacement-range information regarding a displacement range over which the actuator operates to force the variable geometry member between the hard-stop closed position and the hard-stop open position; the reference position is the lowest flow position to which the processing device will direct the actuator to actuate the variable geometry member during normal operation of the turbine the processing device is operative to intermittently direct the actuator to actuate the variable geometry member to the hard-stop closed position, to read the actuation information sensed by the sensor device with the variable geometry member at the hard-stop closed position, and to re-establish the reference-position information by reading the sensor information while the variable geometry member is at the hard-stop closed position, and calculating what the sensor information should be with the variable geometry member at a predetermined angular increment from the hard-stop closed position; and □ the processing device is configured to re-establish the reference position only when newly measured displacement-range information varies from previously measured displacement-range information by at least a predetermined standard. the variation information includes measured displacement-range information regarding a displacement range over which the actuator operates to force the variable geometry member between the hard-stop closed position and the hard-stop open position; the reference position is the lowest flow position to which the processing device will direct the actuator to actuate the variable geometry member during normal operation of the turbine the processing device is operative to intermittently direct the actuator to actuate the variable geometry member to the hard-stop closed position, to read the actuation information sensed by the sensor device with the variable geometry member at the hard-stop closed position, and to re-establish the reference-position information by reading the sensor information while the variable geometry member is at the hard-stop closed position, and calculating what the sensor information should be with the variable geometry member at a predetermined angular increment from the hard-stop closed position; and □ the processing device is configured to re-establish the reference position only when newly measured displacement-range information varies from previously measured displacement-range information by at least a predetermined standard.