An electromechanical apparatus is described that was designed to determine the twist in textile yarns by measuring the number of turns a yarn untwists due to the torque created by a freely rotating axial load. The apparatus utilizes an optoelectronic system to count the number of turns in each direction so that the net number of turns needed to reach the equilibrium state is measured. The damping of the rotating unit was found to be noncritical. A mechanical support system has been designed which facilitates testing and improves reproducibility of results. The system can be used for staple and continuous filament yarns but the sample length for staple yarns must be shorter than the fiber length.