# Evaluation of HMDs by QFD for Augmented Reality Applications in the Maxillofacial Surgery Domain
## 2 Materials and Methods
### Comparison of Market HDMs  
Market research has been carried out to find the current availability of HMD for AR. Then a full comparison has been conducted evaluating the parameters used for the device's datasheets (Table S1). The market offer is not broad, but the proposition is varied. A first and interesting result of the research is the absence of a standardisation of hardware characteristics, and so many different specifications are used in datasheets. Meanwhile, most, if not all, the devices use a standard platform such as Unity(tm) to develop applications and interfaces. Given the diametrically opposed situation of hardware and software, the article will be focused on HMD hardware specifications. The analysis has been done with specifications from datasheets, but macro-specifications will be used in the article for a better legibility. The specifications grouping will be illustrated in Table 1, while a macro-specification explanation is listed below:  
1. Computing power: the horsepower of a device in terms of hardware and software capabilities. 2. Display: device core specification in AR applications. 3. Audio: built-in microphone and earphones. 4. Sensors: device features necessary to get information from the surroundings. 5. File formats: multimedia documents manageable by the device and so the kind of information the user may consult. 6. Connectivity: ports and technologies to connect with other devices. 7. User inputs: ways for the users to control the device. 8. Power: how the device is powered. 9. General features: miscellaneous information about the device. The market research found seven HMD devices following four research criteria: (1) the device must be an HMD; (2) the device must be an AR HMD or, at least, a hybrid AR/VR; (3) the device must be currently available on the market or, at least, in a preselling phase; (4) the device must have an adequate datasheet to refer. The research results show an astonishing absence of medical-oriented HMD. Many projects are under way but far from being commercialised (Oculenz ARwearTM, Beyeonics OneTM, Augmedics XvisionTM) and other products have been already discontinued (Sony HMS-3000 MTTM, Viking Systems HMDTM). Meanwhile, the economists forecast a total of 26 million HMD units sold in 2023 [39] and a growth with a total CAGR (Compound Annual Growth Rate) of 43.8% in the next eight years with the healthcare sector leading the trend [40]; those predictions legitimate the expectation of a growing number of medical-oriented devices in the next years. The devices that meet the research criteria have been gathered accordingly to their general purpose (Table 2), and their specifications have been organised in an ample comparison table available as supplementary material (Table S1). The price of devices varies considerably, showing noticeable steps if products with different purposes are compared. An analysis on devices grouped by purpose has been done to investigate the existence of common traits occurring along each group while has been decided to ignore the price parameter from this point onwards. The first group evaluated has been labelled as industrial tools and contains two devices (Table 3). One of the key points of this group is the use of commercial Operative System (OS), that means the use of a common languages to program. Depth cameras are not a common aspect, while these devices show a robust autonomy and provide some kinds of certifications (e.g., IP67 protection). Good connectivity and audio/video features are a logical consequence of a design oriented towards remote maintenance services. The user input methods are limited to physical buttons and voice commands, features such as eye or hand tracking are not provided but Inertial Measurement Units (IMU) are common. Another distinguishing trait is the ample choice of wearability solutions. The devices of this group are light and compact, and one has a monocular design.