New scales

The box says "linear grating scale" , I assume these are the "glass scales" everyone thinks so highly of - supposed to be .0002" sensitivity . Anyway . I'm wondering what the tolerance for lateral/up-down movement is with these . X and Y are no problem , but the only reasonable place to attach the read head on the spindle has about .050-.060" rotation . I have already designed a guide bushing device to prevent the rotation , but I just got to wondering . How sensitive are these scales ?

I don't know what's inside those scales ... I just know that they're supposed to be much better than the capacitive scales I was using with the old unit . And more expensive too and I don't want to take a chance on breaking one .