Changes

       // set the position to 0:

       // set the position to 0:

       stepper.setCurrentPosition(0);

       stepper.setCurrentPosition(0);

         // Run the motor forward at 400 steps/second until the motor reaches 24 steps (~0.125 revolutions):

         // Run the motor forward at 400 steps/second until the motor reaches 12 steps (~0.125 revolutions):

         while(stepper.currentPosition() != 12)

         while(stepper.currentPosition() != 12)

         {

         {