of the belleville washers 24 with which is device 19 is provided naturally the present invention may be subjected to numerous variations with respect to what is described and illustrated herein without thereby departing from the scope of the invention for example for technological or constructive reasons it could be necessary to position the elastic devices 19 at non constant relative distances in this case there will be deformation differences on the individual segments of the precision beam but the condition that the fastening points all move by the same quantity f is still met by appropriately re dimensioning the rigidities k i with unequal distances between the devices 19 the elastic reactions r i are different in the different fastening points the calculation process shall develop as follows 1 the number of fastening points is decided along with the distance between them and the value of each reaction r i is calculated 2 the reactions r i are applied on the reaction beam and the displacements d i are calculated in correspondence with each point of application of the forces r i 3 a constant displacement f of the precision beam is imposed such that f is greater than the greatest deformation d i f gt d max 4 the rigidity of each elastic element is derived from the relationship k u2062 i r u2062 i f d u2062 i it must be noted that if the distance between the elastic devices 19 is not constant there are variations in the maximum flexion of the prevision beam if the rigidity of the prevision beam is constant along its length it is possible to obtain equal flexion amounts of the precision beam on the bays of different.