This section is from the book "Manual Of Cardboard Construction For Third And Fourth Grades", by Charles A. Kunou. Also available from Amazon: Manual of cardboard construction for third and fourth grades.
With ruler draw AB, 3" long.
With triangle draw lines at right angles with A and B.
Measure BC and AD, 3".
With ruler draw DC parallel to AB.
Test the angles with triangle.
Cut with scissors.
Drill carefully the elements or concepts of the square. Materials: Tagboard or bristolboard.

 
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