The posiioner allows for independent movement of two axis and other than two adjustment screws has no sliding or rolling parts. The bottom and middle plate are hinged on one side. The top and middle plate are hinged on the opposite side. Opposite each hinge is a spring loaded adjustment screw, one that separates the bottom from middle and the other that separates top from middle. The guide scope is attached to the top plate and the bottom plate is attached to the main scope.
Movement is very smooth and the assembly is extremely rigid.
This is a result of the hinges used, they have no stiction friction and no play. The hinges are what I call the poor mans flex pivot or crossed strip hinges. They are very thin metal strips mounted at right angles to each other. Two pieces of metal tape connect the two plates at the corners to make a conventional hinge. But adjacent to each of these strips is another strip of tape, but perpendicular, forming another hinge.