Situation: I am on my feet taking advantage of the meeting's over, and I am cleaning up the blackboard and right behind me is a chair by a desk.
Alternative situations: I am copying the questions on the blackboard and there is a desk on my 6 o'clock direction. Standing in front of a black board and giving my lecture to some students seated on the children.
Question: If I wanted to write on the chalkboard in front of me, what should I use to write?