Nine-tenths of the mechanical work in arithmatic is addition and multiplication and nearly all of the errors occurs in one or the other of these simple operations.

We give here one of the best devices ever invented for training pupils to add rapidly and accurately. Purchase a window shade roller, black oil cloth, and a tube of white paint. Put the figures on in a manner as shown in the cut opposite. By raising and lowering the shade the depth can be increased or diminished. No chalk dust or time wasted in making erasures and writing figures for practice.          Fifteen minutes daily practice for six months with this chart pupils acquire a rapidity of 75 to 150 per minute in addition, their previous speed usually being about 8 to 12 figures per minute.

         Have your children try adding with this chart and time them with a watch and see how many figures they add per minute, note their improvement as it will be something marvelous. The sum can be written with crayon at the bottom of the chart and erased at pleasure.

Source:

 Holst, Bernhart, P. (Teacher, Editor, and Author). 1914. Practical Home and School Methods. Kansas City: The Bufton Book Company. p. 380.