In cases where higher demands exist regarding the precision and long-term stability of machines (for example, in the metrology lab and in production control), special new design approaches must be taken. Aluminum is used as a structural material to improve the controlability of temperature problems. Its high thermal conductivity minimizes differences in temperature, thus reducing deformation of the machines. In order to prevent changes in the tension of the guideway systems caused by expansion, a special system is used in which prestress is produced by means of magnetic force and gravity (Fig.. 29).