## 5 Discussion
### Practical Implications  
Drawing upon the comprehensive analysis of the statistical results and the insights derived from the interviews, we propose the ensuing practical strategies and recommendations for the enhancement of parametric CAD modeling and VR free-form modeling in practical applications:  
1. After decades of interface optimization, the interfaces of current parametric modeling software programs have become graphical ones. However, the rigorous parametric logic of these programs makes learning for design beginners difficult. The enjoyment and emotional response produced by VR technology can reduce design beginners' learning frustrations. Features such as intuitive operation and natural dialogue are recommended to be introduced into future CAD modeling software programs to increase learners' interests and reduce the learning threshold.
2. An advantage of VR interfaces is that they improve self-learning ability. However, in reality, design beginners might be unable to receive instant assistance in device adjustment or software operation. Therefore, developers of CAD modeling software are advised to provide self-learning courses to enable design beginners to familiarize themselves with VR operation without time pressure. Additional prompts and instructions should be provided in the learning process to assist design beginners.
3. Developers of CAD modeling software are recommended to increase the usability of VR devices to increase the ease of learning. For example, the complicated positioning calibration and setting procedures of these devices can be simplified. Furthermore, the popularity of VR devices has increased with decreases in their component size and cost. Software developers should create solutions to increase the usability of and ease of learning with VR devices.
4. The participants suggested that software developers could consider designing customized VR controllers with similar shape, weight, and operation to real pens. Such controllers could also be used to optimize parametric modeling.
5. Some design beginners reported that they experienced slight dizziness after the experiment. We recommend that users should avoid making continual body movements during VR CAD modeling. To reduce dizziness, functions such as viewing angle stabilization and an interface with fixed time and fixed space can be developed.
6. According to the examiners' observations, the participants who had experience in using VR devises exhibited smooth reactions, whereas those who had never used VRdevices exhibited rather unnatural reactions because they required time to familiarize themselves with the operation. The interface operation of those who had experience in 3D modeling was smoother than that of those who had no experience in 3D modeling. The semistructured interviews indicated that those with experience in 3D modeling easily understood 3D spatial concepts, whereas those without this experience required time to understand these concepts, which affected their operational performance. Although VR modeling has intuitive operation, design beginners should receive basic training on 3D spatial concepts, regardless of the modeling techniques that they adopt.