The dependability characteristic of the control software of manufacturing systems is highlighted more than before, going through repeated changes to cope with various and varying requirements. Formal methods are researched to be applied to automation system engineering to obtain a more effective and efficient quality assurance. One of the approaches, a formal specification language named Generalised Test Tables has been developed with the aim of intuitiveness and accessibility for automation application developers. The result of the experiments conducted to assess the usability of this language is presented here. Focussing on evaluating effectiveness and user satisfaction, three paper-based experiments have been conducted with students at the bachelor and master level. The evaluation results point to positive usability in both comparative effectiveness to conventional language, that is, Petri Nets, and subjective perception of user satisfaction.