What are the disadvantages of teaching on a class blackboard?

"padding:0px;margin-bottom:14px;color:#3a3a3a;font-family:Verdana, 'Trebuchet ms', helvetica, sans-serif;font-size:11px;line-height:18px;">

1. Eye to eye contact is lost while writing.

"padding:0px;margin-bottom:14px;color:#3a3a3a;font-family:Verdana, 'Trebuchet ms', helvetica, sans-serif;font-size:11px;line-height:18px;">

2. The written material cannot be stored and reused.

"padding:0px;margin-bottom:14px;color:#3a3a3a;font-family:Verdana, 'Trebuchet ms', helvetica, sans-serif;font-size:11px;line-height:18px;">

3. Advance preparation of material is not possible.