*3.4. Usability Test*

System Usability Scale tests the usability of a product, service, or system using a five-question Likert scale based on responses to ten standardized questions [36]. The test questions are non-complex with responses that include strongly disagree, disagree, neutral, agree, and strongly agree, with index scores ranging from 1 to 5, respectively. The questions are given below for reference. The even and odd-numbered questions in the SUS test reflect a negative and positive attitude. During SUS score calculation, 1 is subtracted from user response for odd-numbered questions, while user response is subtracted from 5 for even-numbered questions. This scales them from 0 to 4 with 4 being the most positive response. Responses for all ten questions for each user is then added, making the sum in the range of 0 to 40. This sum is then multiplied by 2.5 to normalize the response for each user in the 0–100 range. These obtained raw SUS scores can be converted to individual percentile ranking to make relative judgement of usability by normalization or grading on the curve [37]:


The usability test scores breakdown for all participants out of 1–5 (strongly disagree through strongly agree) are given in Table 5. Although the subjects were not accustomed to using their sense of touch instead of sense of vision for perceiving objects. However, positive indices outperform negative indices by obtaining negative scores about half the order of positive overall scores. Here, the positive and negative indices refer to odd and even-numbered questions of the SUS test which reflect the positive and negative attitude, respectively. The overall SUS score of 72.73 converts into the percentile range of 65–69% that ranks at 'Good' objective rating as a measure of user's perception of the usability of system [37,38]. The individually scored SUS results are provided in Figure 7.

**Table 5.** Usability test subject-wise selection for SUS indices.


**Figure 7.** Usability test individual and mean obtained scores.
