If a target or an actual dimension between two components inside precision machines changes, readjustment may be necessary. The disadvantage of classical shims that are ground exactly to the required dimension, is that they need to be inserted mechanically. Furthermore, unlimited fine adjustment is not always possible and once the dimension has been fixed, it is often very difficult to change it afterwards. PI has found the perfect solution for this and developed the PI Rest piezo-based "shims". Once they have been installed into the machine, the active shims not only make it possible to readjust the gap between two components at any time, but also achieve this with nanometer precision.