## 2 Methodology
### User Assignment of Gestures to Commands  
#### 2.5.1 Training and Selection Interface  
Two interfaces were developed using Unity3D (Unity Technologies, San Francisco, CA, USA). One was for training the participants on the commands and the microgestures (Training Interface, Figure 2). The training interface consisted of two parts: (1) pictures were displayed on the left showing a before and after screen image to demonstrate the purpose of the command, and (2) videos of nine microgestures with the other 24 microgestures displayed by clicking the button previous or next page. Once the participants were adequately familiar with the 20 commands and 33 microgestures, they interacted with a second interface that allowed them to review each command, browse the eight pre-selected microgestures, and then select the 2 to 4 microgestures. \begin{table}
\begin{tabular}{l l l l l l l l l} \hline \hline
**Commands** & \multicolumn{6}{c}{**Eight Microgestures Candidates**} \\ \hline Gesture on/off & a & b & c & d & e & h & p & q \\ Open/close menu bar & a & c & e & i & l & q & t & w \\ Scroll left/right & f & g & h & u & v & w & x & y \\ Scroll up/down & d & g & h & r & s & t & u & v \\ Previous/next & f & g & h & s & v & w & x & y \\ Previous/next on a circle & d & e & f & g & i & w & x & y \\ Play/pause & a & b & c & e & h & j & l & m \\ Accept call & a & c & e & f & h & p & v & x \\ Decline call & b & c & d & g & i & q & v & y \\ Mute/unmute & a & b & c & e & h & m & o & v \\ Volume up/down & d & e & f & g & n & r & t & v \\ Marker open/close & a & e & f & h & p & r & t & y \\ Confirm/cancel selection & a & c & e & h & i & k & l & m \\ Shrink/enlarge & a & b & c & d & e & f & g & u \\ Initiate/restore & d & e & f & h & i & n & q & x \\ Cursor & z & aa & ab & ac & ad & ae & af & ag \\ Translation & z & aa & ab & ac & ad & ae & af & ag \\ Rotation & z & aa & ab & ac & ad & ae & af & ag \\ Duplicate & a & c & e & f & h & k & l & v \\ Delete & a & c & e & f & i & l & u & w \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Twenty commands with eight pre-selected microgestures (gesture numbers from Figure 1). Figure 2: Interface for training participants on the command (task) and all the designed microgestures displayed on the computer monitor. tures that best matched the command (Figure 3a). The selection was based on the personal experience of the participant and their interaction habits with prior smart devices (phones, tablets, etc.). For example, for the command \"scroll left/right\", the highest-ranked gestures matched the direction of the command, such as gesture w (index finger scrolls left/right with the pronated forearm and the hand in index fist posture, Figure 1). After selecting the 2 to 4 microgestures for a command, participants rated each selected microgesture on four characteristics, preference, match, comfort, and privacy, using an 8-point Likert scale (0 = low, 7 = high, Figure 3b). Preference was used to rate the microgesture from most to least preferred. Match indicated how suitable the microgesture was to complete the command. Comfort indicated how easy or comfortable the microgesture was to perform repeatedly. Privacy indicated how easily bystanders could notice the microgesture if performed in a public setting, with higher scores associated with a higher level of privacy. The four characteristics were defined for each participant before the microgestures were rated. The ratings for comfort and privacy were for the microgesture and not the command; therefore, theoretically, these ratings should be the same when selected for different commands. Participants were also encouraged to demonstrate their own unique microgesture for a command or they could select a microgesture from the 33 microgestures if it was not represented among the eight pre-selected microgestures. If they demonstrated a new microgesture, it was video recorded via ZoomTM (San Jose, CA, USA).