casting mold in which the mixture is compacted by suitable vibrators and hardened that then results in the cast block required for providing the machine bed 4 in the casting operation the fixing means for example in plate form for columns and pillars of the measuring apparatus are simultaneously cast into the cast block which is produced in one piece together with the above mentioned fixing means 12 and 14 and the guide rails 13 in the illustrated embodiment in fig1 the tire 1 to be tested is arranged horizontally in the measuring apparatus but it will be appreciated that it is also possible to use the machine bed 4 consisting of the cast polymer concrete block in a measuring apparatus such as a tire testing machine in which the tire is disposed in a vertical position referring now to fig2 and 3 shown therein is an embodiment of an apparatus according to the invention in the form of an unbalance measuring apparatus in which a rotary member in the form of a rotor indicated at 25 can be mounted in a horizontal position rotatably about an axis as indicated at d in a rotor mounting arrangement comprising two mounting stands or supports 16 and 17 fig2 is a.