## 4 Conclusions  
Single markers suffer from numerical instability, particularly when they are small within the camera image. To address this, our study introduces a two-step calibration model that leverages multiple markers for accurate localization in a larger indoor environment. We put our model to the test using the MS Hololens AR device, which traditionally relies on SLAM for tracking. Notably, our experiments were conducted in an industrial setting to investigate how markers impact the accuracy of 3D point measurements. We meticulously measured four distinct points in both the physical and augmented reality realms. Our findings reveal that employing two markers significantly reduces angular discrepancies between points in the real and augmented environments. This is made possible by our novel model that deploys two fiducial markers aligned along the x-axis in a virtual space, effectively doubling the measurement data for precise alignment. Moreover, our results underscore that registration accuracy improves as the number of calibration points increases. Thus, our study establishes quantitative forms and parameters to compare the calibration models of AR solutions. The discussion of the results obtained stimulates the production of studies and quantitative analyses of AR solutions. This study establishes numerical criteria for evaluating the proposed models, enabling direct comparison of results with future experiments and with different devices. Future generations of HoloLens or other similar AR devices will likely include sensor improvements. However, the calibration and positioning method proposed in this study is based on general concepts and assumptions about AR. Although the experiments were performed on a first-generation HoloLens, the perspective is that future generations of AR devices will also be able to benefit from the results of the two-step calibration process proposed in this study. One factor that directly influences precision is the angular distance. Here, the two-step calibration proposed in this study has a significant influence. The tests allow us to conclude that the two-step calibration increases the precision compared to the simple calibration, and it also is more suitable for use in industrial scenarios where the localization of objects with high precision is required. Some hypotheses of contributions of the calibration model proposed in other research [20] help to exemplify the possibilities of practical applications of the two-step calibration model. These hypotheses open new lines of investigation and, consequently, new opportunities for studies. Some factors may negatively influence HoloLens behavior in specific circumstances, such as the inadequate functioning of the HoloLens in sunlight. These are device limitations reported by Microsoft itself in the equipment documentation. Therefore, this study avoided carrying out the experiment in circumstances that would obviously be frustrated due to the limitations of the equipment (not the proposed calibration model). Although the research carried out is inspired by the demands of the industrial sector, the calibration method proposed in this study is not limited to this context alone. AR systems with critical precision and accuracy in displaying holograms can benefit from the results achieved in this study. The two-step calibration model proposed in this study fulfills the general objective of this research and answers the guiding question. Its application in HoloLens presented precision and accuracy values in displaying holograms that were significantly relevant in comparison to the volume of the environment used in the experiment. The two-step calibration model proved to be effective for HoloLens applications in industrial and similar contexts. Conceptualization, J.S.N. and F.B.C.A. ; methodology, J.S.N. and I.W. ; software, J.S.N. ; validation, I.W. and V.d.S. ; formal analysis, J.S.N. and V.d.S. ; investigation, J.S.N., L.S.V.S., V.d.S. and V.M.S.O.S. ; resources, A.A.B.S. and I.W. ; data curation, J.S.N., F.B.C.A. and V.d.S.