The later English artists have somewhat changed the mode of communicating motion to the slides, by attaching the screws pdrmanently to the micrometer head and tapping each micrometer screw into its slide.
One reply to this is that it is not difficult to determine from time to time the errors of the screws and to apply the necessary corrections to the observations.
Balls Theory of Screws an analysis is made of the possible displacements of a b~dy which has respectively two, three, four, five degrees of freedom.
Ball's paper on the Theory of Screws, published in 1872.
The base plate rests upon levelling screws which permit the adjustment of the polar axis to be made with great precision.