The modular design of the Absolute allows for quick and easy upgrades. Due to the precise design of the Absolute you can change camera arms as often as you wish without ever effecting the accuracy of the head.
The camera arms are used to set the entrance pupil (nodal point) of the lens. The accurate setting of the entrance pupil allows for error free stitching and can also improve the accuracy of automatically generated control points.
Shown below is the new knob registered D2X / Nikkor 10.5DX camera arm.