## 2 Research Methodology
### Paper Selection  
For the systematic search of documents, a set of search strings was determined to search the databases mentioned in the planning phase. The Search strings and search syntax for each database are listed in Table 2.  
Comparing to assembly and maintenance, the AR-based applications supporting the quality sector have not been comprehensively investigated in the last few years. Thus, assembly and maintenance sectors can be considered as good references for the development of AR-based quality control applications. In addition, assembly, maintenance and quality control are normally carried out in similar working conditions and all require intensive \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Database Name**} & \multicolumn{2}{c}{**Search Strings**} \\  & & **[Search: by Title, Abstract, and Keywords]** \\ \hline \multirow{5}{*}{1} & & TITLE-ABS-KEY ((“augmented reality” OR “mixed reality”) \\  & & AND (“industry 4.0” OR “manufacturing” OR “Production” OR “factory” OR “factory” OR “industrial application” OR “quality” OR “assembly” OR “maintenance”)) & OR “Traditional application” OR “Manufacturing” OR “Production” OR “factory” \\  & & AND (LIMIT-TO (DOCTYPE, “ar”)) \\  & & AND (LIMIT-TO (LANGUAGE, “English”)) \\ \hline \multirow{5}{*}{2} & & (TS = ((“augmented reality” OR “mixed reality”) \\  & & AND & \\  & & (“industry 4.0” OR “manufacturing” OR “Production” OR “factory” \\  & & OR “industrial application” OR “quality” OR “assembly” OR “maintenance”)) \\  & & AND LANGUAGE: (English) \\  & & AND DOCUMENT TYPES: (Article) \\ \hline \multirow{5}{*}{3} & & (“augmented reality” OR “mixed reality”) \\  & & AND (“industry 4.0” OR “manufacturing” OR “Production” OR “factory” OR “industrial application” OR “quality” OR “assembly” OR “maintenance”) \\ \hline \multirow{5}{*}{4} & & 1 st search: \\  & & (“augmented reality” OR “mixed reality”) \\  & & AND (“industry 4.0” OR “manufacturing” OR “Production” OR “factory” OR “standard” OR “maintenance”) \\ \hline \multirow{5}{*}{4} & & 1 st search: \\  & & (“augmented reality” OR “mixed reality”) \\  & & AND (“industry 4.0” OR “manufacturing” OR “Production” OR “factory”) \\  & & 2 nd search: \\  & & (“augmented reality” OR “mixed reality”) \\  & & AND (“industrial application” OR “quality” OR “assembly” OR “maintenance”) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Database query strings. involvement of the operators. Therefore, keywords such as \"assembly\" and \"maintenance\" are included in the search strings besides keywords such as \"manufacturing\", \"industrial application\", etc. After systematically searching with the above search strings on respective databases, there were 1248 documents found (see Table 3). On the left side of Figure 3, a chart referring to the numbers of publications is illustrated, which were systematically found on databases. The large number of articles found using databases were from Scopus (38%) and WoS (36%). Regarding duplication, 78% of found articles only belong to one single database, 18% to two databases and 4% to three databases shown on the right side of Figure 3. In addition, the manual search resulted in 48 more articles by scanning cited references of influential review papers. The AR articles were selected and approved based on the following criteria described in Table 4: Inclusion and exclusion criteria. The number of publications excluded referring to specific criteria were also included in the table. The relevant exclusion criteria were applied for each stage of paper selection flowing PRISMA flowchart as in Figure 4.  
The main strategy for paper selection following the adapted PRISMA flowchart is intensively applying exclusion criteria for the first screening and full-text eligibility evaluation. If a paper meets any exclusion criteria, it would be immediately excluded from the search results. The inclusion criteria were used for the second screening to check the quality of articles.