In measuring transverse deformations (Poisson coefficient) of structural materials it is necessary to solve several additional problems as compared with longitudinal deformation measurements. It is then necessary to provide a (three-four times) higher measuring equipment sensitivity, since the transverse deformation e z is considerably smaller than the longitudinal one e r and in particular the ratio of sz/el for the majority of structural materials amounts to 0.15- 0.3. For a reliable determination of transverse deformations in cylindrical specimens it is necessary to measure the specimen's diameter in at least two directiom, in order to eliminate the effect of ellipticity which can result from repeated deformation and application of eccentric loads. These factors have to be taken into consideration especially when the deformation diagram has a yield plateau and when tubular specimens are measured. We have developed a strain gauge for measuring transverse deformations (Fig. 1) which eliminates the above factors. It consists of the flexible tape 1, made of a 0.04-mm-thickste el foil, the movable bracket 4, hinged to the support 3, the measuring head 5, and the pin 2 for fixing the tape to the measuring stem of the head and to the bracket. In placing this equipment on the tested specimen, the support 3 is fixed to the casing of the longitudinal deformation strain gauge [1] and the tape 1 firmly wound round the specimen in one turn. The measuring head(Fig. 2) consists of a capacitive displacements transducer of a differential type and comprises the casing 1, two stationary rings 2, which are insulated from the casing by the bushing 5, the measuring stem 6, and the shield 4. The casing 1 is provided with openings for leading in and soldering wires to the stationary rings 2. The measuring effort of the stem 6 is produced by the spring 3 and amounts to 0.5-0.7 N. The displacement of the measuring stem produces changes in the capacitance between the stem and the stationary rings, and this serves as a measure of the tested displacement. The strain gauge operates in the following manner: changes in the tested specimen's diameter moves theends of the flexible tape, and their relative displacement is registered by the measuring head. The signal produced by the measuring head is recorded on a bridge circuit similar to the one described in [2]. Since the specimen is gripped by a single turn of the tape and its ends leave the specimen's surface along the same straight line, their relative displacement coincides with variations in the length of the specimen's external circumference at a given cross section and the ellipticity of the specimen does not affect measurement results. The hinged fixing of the bracket 4 (see Fig. 1) ensures equal tensile forces at either end of the tape; thus providing a symmetrical sapping of the tape over the speeimen's surface with respect to the point opposite to the tape crossing point. Owing to this arrangement the area of the unidirectional slipping of the tape is reduced to half the specimen's circumference, thus decreasing the backlash due to friction.