

School Scrambles To Preserve Newly Discovered Chalkboards From 1917 - watto1
http://www.npr.org/2015/06/23/414616431/school-scrambles-to-preserve-newly-discovered-chalkboards-from-1917

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dang
[https://news.ycombinator.com/item?id=9673347](https://news.ycombinator.com/item?id=9673347)

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Mithaldu
Of course someone on Reddit already has an answer:

[https://www.reddit.com/r/AskHistorians/comments/38u3av/how_d...](https://www.reddit.com/r/AskHistorians/comments/38u3av/how_did_this_multiplication_wheel_from_a_1917/crye1o0)

