927 may be segmented and sealed with the differentially pumped grooves 928 and lands 926 completely surrounding them one potential embodiment of a quad scan motion system could employ dual y axis drives 905 and a single x axis drive 906 this type of stage actuator is common in the art of single plane xy air bearing systems for ambient pressures and would allow for driving on the center of mass and measuring on the plane of the wafer a wall down the center 905 gives structural column support to the base reference member 913 and sub base plate 914 against the atmospheric pressure they would be exposed to this wall 905 would also provide structure for mounting motors feedback positioning cooling and other services a shuttle system 903 can be u2018 handed u2019 a stage 902 by the xy motion system 905 906 the shuttle 903 may then translate the stage 902 with functionality switching the stage 902 from one xy system and process to another the machine may have only two or three stages as in fig9 c or it may have five or more xy systems and processes there must be conductance between the top side of the stage 902 vacuum volume 929 and the volume 931 on the underside of the stage 902 as shown in figure 9 b the holes 930.