Table 1 Sample feedback provided by the subject experts

1. Arrange topics in fundamental order to expertise manner

2. Omit sphere part and auxiliary plane part

3. Projection of line is most important

4. Conic Section, projection of lines, and projection of planes are important topics

5. Suggested to include Isometric View contents

6. Visualization and handling large number of students in classroom, are most concerned issues in ED

7. The projection of a plane is more important compared to the projection of lines

8. Suggested that app could be helpful for students

9. According to demonstration of contents in ED is difficult with the help of slides, materials available on YouTube is sometimes insufficient