{HEAD ~ Interferometers} 341 and 342 generate electronic signals 347 and 348, respectively, which are transmitted to {TAIL ~ electronic controller} 350 where they are processed to determine the position of stage 320 in the x direction and changes in the angle of bar mirror 346 in the plane of FIG 3 
{ HEAD ~ Interferometers } 341 and 342 generate electronic signals 347 and 348 , respectively , which are transmitted to { TAIL ~ electronic controller } 350 where they are processed to determine the position of stage 320 in the x direction and changes in the angle of bar mirror 346 in the plane of FIG 3
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