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Mathematical Treasure: Blackboard-Sized Triangles

Amy Ackerberg-Hastings (University of Maryland University College)

Two blackboard-sized drawing triangles by Safe-T.

Two Safe-T Blackboard Triangles, Model Number 42123, 2000, Smithsonian Institution negative number DOR2012-8017.

In the 20th century, instrument makers began to provide mathematical calculating and drawing instruments in over-sized versions so that teachers and professors could use them at the blackboard. By the end of the century, some manufacturers had become concerned that traditional materials, such as wood or metal, could injure young school pupils. They turned to plastic because it was durable but also because it was soft and could be molded into shapes with rounded edges and corners.

This object and other set squares, T-squares, and drawing triangles from the Smithsonian's National Museum of American History are now shown and described at the website

Index of Mathematical Treasures

Index of Mathematical Objects

Amy Ackerberg-Hastings (University of Maryland University College), "Mathematical Treasure: Blackboard-Sized Triangles," Convergence (September 2014)

Mathematical Treasures: Smithsonian National Museum of American History Object Groups