## 4 Results: Analysis of the Integration of VR, AR, and MR in the Design Process
### Results of Usability Indicator Analysis
#### 4.1.3 Interoperability  
During the development of the Design Units, the functional interoperability between the VR devices used and other digital software and hardware platforms ('iPad', 'Stylus Pen', 'Ultimaker Cura', 'Procreate', and 'Keyshot') was analysed. OBJ or FBX files were used as standard formats for model transfer, although adjustments to scale and alignment were sometimes required to ensure proper visualisation or manipulation in the target platforms. In Design Units 1 and 2 (ring and candle holder), for example, files were exported in OBJ format to check the print parameters in 'Ultimaker Cura' and manufacture prototypes using a 3D printer (Figure 4b,f). This process required a specific review of the scale and orientation to ensure the technical feasibility of printing. In Design Unit 4 (mouse), the workflow began with preliminary modelling on an iPad Pro (Figure 5a) using the device-specific version of 'Gravity Sketch', allowing high precision with the digital pen and flexible tactile interaction (Figure 5a). The file was exported in OBJ format and imported into 'Procreate', where complementary details were added using 2D digital sketching (Figure 5b). The mouse design was then finalised in VR with 'Gravity Sketch' by generating surfaces on the previous structure and selecting the appropriate colours (Figure 5c). This process enabled the achievement of high-quality graphic output for conceptual presentations (Figure 5d). The transition from 'Gravity Sketch' to 'KeyShot' was implemented in Design Units 5 (outdoor armchair) and 6 (reading armchair) using the FBX file format. The ability to retain geometry, textures, and colours applied within the immersive environment avoided the need for manual reassignment of materials and accelerated the rendering process. The outdoor armchair was rendered in 'KeyShot' (Figure 6a). In the reading armchair Design \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Design Units** & **S** & **F** & **R** & **I** & **L** & **T\({}_{\mathbf{e}}\)** & **T\({}_{\mathbf{t}}\)** & **Human Error (HE)** \\ \hline
1. Ring & 1 & 4 & 3 & 20 & 10 & 1 & 2 & 0.03 \\
2. Candle Holder & 1 & 8 & 10 & 5 & 5 & 5 & 7 & 0.03 \\
3. Vehicle & 1 & 5 & 4 & 10 & 5 & 1 & 1 & 0.04 \\
4. Mouse & 1 & 6 & 5 & 9 & 4 & 1 & 8 & 0.04 \\
5. Outdoor Armchair & 1 & 5 & 8 & 4 & 5 & 2 & 6 & 0.04 \\
6. Reading Armchair & 2 & 14 & 3 & 2 & 3 & 1 & 8 & 0.08 \\
7. High Stool & 4 & 15 & 4 & 3 & 3 & 2 & 8 & 0.14 \\ \hline \hline \end{tabular}  
* S: successfully completed tasks; F: errors or incomplete tasks; R: restarts due to loss of control or serious errors; I: interruptions caused by interface difficulties; L: loss of work control; T\({}_{\mathbf{e}}\): total time spent correcting errors; T\({}_{\mathbf{t}}\): total time to complete tasks (including errors).  
\end{table} 
Table 6: Analysis of human error in Design Units. Figure 5: Interoperability process of mouse design: (**a**) 3D sketching with Gravity Sketch for iPad; (**b**) presentation sketch with Procreate for iPad; (**c**) surfaces and colour generation with Gravity Sketch for computer; (**d**) final mouse design. Unit, materials were assigned in 'Gravity Sketch' (Figure 6b) and successfully retained in 'KeyShot' (Figure 6c). Further material and finish tests were performed in the rendering software for each of the designed models (Figure 6d). For Design Units 1, 2, 4, 6, and 7 (ring, candle holder, mouse, reading armchair, and high stool), the design outcomes were integrated directly into MR using 'Gravity Sketch'. The models were visualised at full scale in the physical environment to verify the dimensions of the ring (Figure 7a), create the revolved surface of the candle holder (Figure 7b), visualise the mouse and check the dimensions using a real hand (Figure 7c), and analyse the spatial and aesthetic integration of the reading armchair (Figure 7d) and the high stool (Figure 7e)).