On this picture you see the frontend of the microscope (the electronics is mounted in the main rack) on it's mount. The thick cable going to the microscope is fiber optic cable that supplies the illumination of the field of view. The yellow vertical device is the rod to be calibrated. This picture shows one of the new types with it's bar code marking. These kinds of rods are no longer designed to be "human readable". Instead they are used in conjunction with a special digital level.
When you look closely you see that the rod is mounted into a black carriage (two of the holding screws you see a little bit above the microscope). This cariage is moved up and down on a stable guide by a motor and a spindle. To get an impression of the dimensions: The part of the rod you see in the picture is about 60cm. The whole rod is about 4m in length, so the space needed for the guide is more than 8m. It extends over two stories in the building (the ceilings are really so high in the old part of the university).
What is invisible here is the underside of the mount for the microscope. There, exactly under the microscope, is the reflector for the refernce beam. Should the mount change it's position by any means this setup compensates for that (Abbé's principle).