An apparatus comprising a drive server, a control server and one or more decoder devices. The charged particle beam is deflected by the first deflector to intersect the optical axis. The comparison fails when the first form is not comparable to a value derived from the second form. The control unit produces test signals and transmits the test signals to, and receives tests signals from, the test fixture. A Z pole guide on the base unit may be extended by adding expansion guide poles that guide the movement of the robotic system through the library.