ARA designs and manufactures the ACU-3D ‘x’ ‘y’ – ‘abc’ series of positioner controllers that are supplied with nearly all of our systems. The current series is based upon a feedback based command and control structure that ensures the commands sent are received and acted upon accurately. The ‘x’ variable in the model number indicates the number of axes controllers contained within the ACU unit. One to three are typically available. The ‘y’ variable indicates the height of the 19″ rack in standard 1.75″ units. A typical dual axis controller would have the following model number: ACU-3D-24. Additional designators would specify any additional options included such as preamp bypass control, polarization options, etc.