A power saving method for rotating pulp and paper machinery includes a fiber quality measurement device, a control system and a variable speed drive. The power savings method is applied to either fiber refiners or pressurized screens. Pulp stock enters a rotating machine, which is driven by an electric motor. The electric motor receives electrical current from the variable speed drive to implement rotation. The variable speed drive changes a frequency of the electrical current according to input received by the control system. The control system includes a control algorithm to optimize the efficiency of the rotating machine. The control system receives inputs of pressures, flows, consistency and position. The control system also receives input from the pulp quality measurement device. The algorithm calculates the process values and input from the pulp quality measurement device to determine the appropriate electrical current frequency to output to the electric motor.