Everyone has experience of wiping blackboard in schooldays, that is quite tiring when we use the eraser cleaning it each time. The blackboard and erasers have basic functions on teaching, but the shortcoming is chalk dust produced, it is not a good idea for teaching quality.
Especially the blackboard always cleaned by teachers and students, it is harmful to health even more. And above all, too much lime which enters the lung to make teachers get more risk of chronic lung diseases, students ...
Especially the blackboard always cleaned by teachers and students, it is harmful to health even more. And above all, too much lime which enters the lung to make teachers get more risk of chronic lung diseases, students ...
Taiwan