## 3 Materials and Methods
### Usability  
Participants were asked to complete the popular SUS (System Usability Scale) questionnaire [45, 46] to establish their perceptions and measure usability for the AR app on a smartphone. To make the questionnaire more user-friendly pictograms were used on the response scale for each question, as suggested by [PERSON] et al. [47]. According to [PERSON] and [PERSON] [48], usability studies using the SUS should have sample sizes of at least 12; because of this the 16 participants of the AR Group answered the ten questions on the SUS (System Usability Scale) (see Figure 3). Interpreting scoring can be complex. \"The participant's scores for each question are converted to a new number, added together and then multiplied by 2.5 to convert the original scores of 0-40 to 0-100. Though the scores are 0-100, these are not percentages and should be considered only in terms of their percentile ranking\" [46]. SUS is a highly robust and versatile tool for usability professionals and based on research, a SUS score above a 68 would be considered above average and anything below 68 is below average, however the best way to interpret your results involves \"normalizing\" the scores to produce a percentile ranking [49, 50]. An average score of 77.5 out of 100 was obtained from SUS questionnaire administrated at participants of the AR Group, which indicates that the app has fairly good user-centered design. In interviews with the AR group important qualitative information was obtained about the experience associated with the new prototype. The term \"application\" will be used to refer to the complete prototype--this includes the lesson elements and the mobile device application _Augment Sales_ used to view the 3D models. The two sessions conducted with each of the experimental groups were completely recorded--experience, feedback and completion of the SUS questionnaire. The two sessions carried out with each of the experimental groups were completely recorded--experience, feedback and completion of the SUS questionnaire. In addition to SUS questionnaire, three questions were asked of all AR group participants to obtain extra feedback:  
* Question #1: How much do you like the application? It is entertaining, boring, it attracts attention, you don't like it. * Question #2: Have you been surprised by the virtual 3D drawings integrated into the real environment? * Question #3: Did you find it difficult to use the app? * Question #4: Would you like to have more AR apps to study or do you prefer the video version? Regarding the emotions associated with the application, fourteen participants consider the overall activity as entertaining (Question #1). Among the many responses made by participants at Question  
Figure 3: Comparison of the adjective ratings, acceptability scores and school grading scales, in relation to the average SUS score [49]. #2, one in particular stood out--a high-comprehension participant stated that the surprise element of the application (projecting unfamiliar images) kept her interested and attentive. However, this same element produced a different feeling in a participant with low reading comprehension, who stated that he did not like having to wait to be able to see the image (referring to the time taken between scanning and projecting). Five participants indicated that they were not surprised by the way they visualized the 3D models, because they had already seen similar applications on social networks. However, nine participants considered it a novel way of watching and listening. When asked about the most frustrating moment of the test (Question #3), all participants indicated that they did not encounter any particular difficulty when using the application. It should be noted that all AR participants tested the application prior to starting the experiment. Despite some encountering complications when scanning the first models, they generally improved with practice.