Round chalk crayons are used in the compasses to draw circles, but hand lines drawn with them are not so neat as those produced with the square-shaped chalk.
To obliterate or remove the construction, or false lines made on the blackboard, a wooden handle two inches in diameter with a cone end 3 or 4 inches long, covered with chamois skin or soft cloth tightly wrapped round the cone and fastened with a tack or drawing pin, makes the best implement to erase lines not required, the point of the cone will remove these without destroying the lines or curves which meet them.
Sponges, chamois skin or cloth rubbers are used to rub out the chalk drawings and clean the blackboard.
The best height for a diagram on the blackboard is not higher than the head, nor lower than the elbow.
Horizontal lines should be made from the left to the right; the body and arm being moved with the hand, and kept in the same relative position with it, will steady the hand.
Curved lines to the left should be drawn first, enabling the eye to take in not only the curve in process of formation but that already made.
Passing the crayon in the hand, over the intended curve previous to marking it, will guide the eye and give confidence to the hand in chalking the curve.
A proper distance from the blackboard is essential, the face being about two feet away from it.
Draw with the whole arm extended from the shoulder-joint, not from the elbow or wrist.
