1. Enables students to clear demonstration purposes, requirements and process, and let them know what to watch, how to look, what problems they have to consider ,make them active, positive, consciously observe and think.
2.Exquisite demonstration method. Demo will closely cooperate with teaching in time,and taking visual teaching tools too early or too late will scatter students' attention. During the presentation to the students, teachers' questions, or appropriate explanation and guidance guide them to see and listen while thinking to obtain the best effect.