## 2 Related Work
### Industrial Training in VR  
Industrial maintenance, assembly, and installation is one of the largest application fields of VR and may greatly benefit from adopting VR technologies. The major application is split into two areas: (1) pre-job training and (2) on-site support [2]. VR-based pre-job training is a well-studied matter, which demonstrates positive effects on the performance and accuracy of maintenance technicians coupled with a decreased error rate and training time [6; 7; 8; 20; 29]. A study by [PERSON] et al. [11], for instance, demonstrated that after 20 min of training in VR, participants were able to perform maintenance operations over a real-world dosing pump. Nevertheless, their study showed significantly better performance of traditional hands-on training methods (pairwise and video training) over VR training, indicating that VR training should supplement, rather than replace, traditional methods. From the perspective of elevator manufacturing and maintenance companies, such as KONE, and supported by existing research in the field, VR training has clear benefits for the industry. First, it provides a safe environment for learning safety-critical tasks [2; 30]. The learner can also repeat the task several times if needed, opposite to, for example, real-life installation tasks, which can be conducted only once per installed product. Another explicit benefit of VR training is the possibility of practicing the installation and maintenance of a brand-new product that has not been physically built anywhere yet, which results in the installers being better prepared for the first installations. Further, VR training modules can also replace expensive physical simulators that are only available in a few locations and require learners to travel--whereas the substituting VR training modules are available everywhere with the VR sets. Additionally, many elevator components are large and heavy (e.g., a big motor weighs several thousand kilograms), thus making real-life maintenance tasks physically demanding, whereas VR training is physically light and requires no additional physical workload. The efficiency of industrial training is linked to the concept of training transfer--the ability to transfer and apply gained (during the training) competencies, knowledge, and skills to the real-job task. The quality of training transfer depends on two factors: learner characteristics and intervention design and delivery [31]. The concept of transfer overlaps with existing theories, present in the educational domain--for instance, with deep and meaningful learning. Deep meaningful learning, defined by [PERSON] as \"the higher-order thinking and development through manifold active intellectual engagement\" [32], where meaning is created based on concept association and pattern recognition, comes from the combination of deep learning and meaningful learning approaches. The use of technology can advance deep meaningful learning activities when used as a base for teaching and learning strategies to support discussion, cooperation, and knowledge creation [32], e.g., affecting intervention design and delivery of transfer via technology. The strength of learning in immersive virtual environments comes from gaining specific context-sensitive knowledge in simulated spaces, which enables active learning [31] and helps to transfer and apply gained skills to real-life situations [9]. This, in turn, advances both content relevance and practice, and feedback variables of intervention design, increasing the quality of training transfer [31]. In the context of industrial maintenance and assembly, such processes may be also referred to as a knowledge transfer from experts to learners. VR, due to realistic simulations and experiences, enhances the effects of knowledge transfer from the virtual world to the real as well as positively affects situated learning by immersing the learners in a virtual space in which specific knowledge can be acquired [9]. The article by [PERSON] et al.