Abstract: This device for detecting possible distortions in a frame or in the base of a chassis-cum-body of a motor vehicle or other frame structures comprises a pair of carriages slidably mounted on rigid support members, each carriage having pivotally and separately mounted thereon a pair of arms carrying measuring rods at their outer ends, each arm being rigid with a toothed wheel so that the toothed wheels of each pair of arms mesh with each other and the arms constantly form symmetrical angles, like the two legs of a compass, irrespective of their positions, in relation to the longitudinal center line of the device which, for checking the presence of possible distortions in the frame or body base, is caused to register with the longitudinal center line of the frame or body base, whereby the measuring rods may be caused to register with predetermined reference points of the frame or body base.