(b) Adjusting volume

**Figure 6.** Animation screenshots of mechanical simulation for Idea 1.

#### (c) External source (iPhone/USB)

**Figure 7.** Animation screenshots of mechanical simulation for Idea 1.

In order to carry out the usability experiment, videos of the mechanical simulations for Idea 2, 3, 4 were also prepared. After these videos were ready, the next step was to design the questionnaire for the participants including potential customers, managemen<sup>t</sup> and design team. The highlights of this questionnaire are as follows:

