https://www.sciencedaily.com/releases/2019/09/190919093940.htm

Scientists at the Institute for Frontier Science Initiative, Kanazawa University, conducted the current research in collaboration with a scientist from Tokyo Metropolitan University. Ten students participated in the experiments. The height of the touch screen was set as 50, 65 or 80% of each participant's height. The tilt angle of the touch screen was set as 0 (horizontal), 45 and 90 degrees (vertical). The size of the touch screen buttons was 10, 20 and 30 mm. For screen visibility, a subjective scale for the individual participating students was adopted. The physical workload was quantified as joint torque ratio*2) (JTR) calculated after measurements of the angles of joints, i.e. neck, shoulder, elbow, wrist, waist, knee, and ankle.

The Pareto optimal solution using those data showed ranges of 1124-1251 mm for the absolute height and 44.4-67.9° for the tilt angle. Concerning the size of the characters, the larger size showed better visibility; 20 mm buttons proved to be enough in practice. The visibility was reduced, however, when the size was 10 mm.