## 4 Discussion
### Subjective Evaluation of the Prototype: ASQ, UEQ, and SUS  
Although the experts with the VR prototype were less satisfied with task performance and the required time (ASQ) than the experts with the real prototype, both the user experience (UEQ) and user acceptance (SUS) were rated better. However, significant differences were only identified for the _efficiency_ dimension of the UEQ. The _efficiency_ dimension was rated significantly to be better by the VR drilling experts group. Since the VR prototype was operated with controllers and lacked important feedback components such as force feedback, the operation of the VR prototype was expected to be rated worse.  
One reason for the overall higher subjective rating of the prototype could be the novelty effect [45; 46]. In this effect, participants evaluated new products better, owing to the novelty of technology, and showed increased motivation. None of the participants had experienced VR before the test. Further studies should investigate whether the use of VR leads to bias in the results owing to the novelty effect. For example, a product can be evaluated by user groups with no VR experience, with little VR experience (<10 h), and with a lot of experience (weekly use). If the experience with VR systems has a significant effect on the subjective evaluation of a product, it is an indication of the novelty effect. Consequently, only participants with extensive VR experience should be recruited for future VR user tests. This could lead to problems in recruiting participants, and highlights the need for further studies to investigate whether prior VR training can attenuate the novelty effect.  
Only a few studies have investigated user experience and acceptance of products in VR and compared them with real products. In a study by [PERSON] and [PERSON] [2], users who were presented with a product on an HMD rated it significantly better than those who were shown the product on a monitor. [PERSON] et al. [47] studied the user experience of three furnishing products in VR and real-world settings. For two of the three products, there were no significant differences in the user experience ratings. One product was rated as significantly better in VR. Overall, the existing literature and our study suggest that the user experience of products and prototypes tends to be rated better in VR [48]. This should be considered particularly for products where the user experience is crucial for product success, such as consumer products.  
[PERSON] and [PERSON] [49] revealed that participants rated the usability of visually attractive products to be better. To prevent this, the VR and real prototypes used in our study were based on the same computer-aided design files. In addition, we ensured that the color schemes of the two prototypes were identical.  
User acceptance of the new prototype was determined using the SUS. The SUS is used to measure the usability and acceptance of a product. Studies recommend a sample size of at least 30-35 participants to obtain reliable results [50; 51]; however, to identify the differences between different products, 8-12 participants were sufficient [52]. Owing to the small sample size and high standard deviation of the questionnaires in terms of usability, significant differences were not expected between the SUS scores. Nevertheless, the SUS scores of the novices and experts were relatively close (SUS\({}_{\text{Ex}}\) = 83.6 \(\pm\) 15.8; SUS\({}_{\text{Nov}}\) = 77.3 \(\pm\) 13.9). [PERSON] et al. [53] revealed that novices have difficulties in estimating aspects such as the size, weight, and material of virtual prototypes. The novices operated the drilling rig for the first time; therefore, they could not compare the prototype with existing products. It is unclear whether the prototype convinced the novices, or if the novelty effect influenced the results.